Three methods of determining extinction coefficients of light in sea water have been compared: (a) on water samples contained in a Pulfrich photometer, (b) from brightness profiles determined by aerial photographic survey, and (c) by photoelectric underwater measurements. The ratios of extinction coefficients for green and red light as determined in 1945 by the Pulfrich photometer and by the brightness profile method are given in Table 3, columns 9 and 10. For green light the ratio is about i-8 and for red light 1-3.

The departure from unity is attributed to the geometry within a confined tube and, within the Pulfrich measuring assembly, of light rays scattered forward by particles present in sea-water samples. In the following year, 1946, comparisons were made between the Pulfrich method and the submarine photometric method of Atkins and Poole. The discrepancies were variable and even larger, the ratios averaging 3-8 for green light and 2-0 for red light.

The brightness profile and submarine photometric methods have not been directly compared, but, by comparing the two sets of determinations against the Pulfrich photometer, it would seem that extinction coefficients determined with the brightness profile method are about 2-2 times those determined by the submarine photometer in green light and about 15 times in red light.

Anew species of deep-water txachymedusa from the North Atlantic is described and named Colobonema apicatum. Most specimens occurred deeper than 1500 m.

The dependence of prevailing wind drift in the Celtic sea upon prevailing winds is discussed and a proposal made to use wind records for the Scilly Meteorological Observatory for assessing drift currents for use in biological investigations.

If there is no seasonal change in the direction of the prevailing winds, nevertheless, the wind drift in summer will be more northerly than in winter.

The terms ‘current’, ‘residual water movement’ and ‘drift’, as used in this series of papers, are denned. The Ekman–Thorade equation for computing wind drift from wind is discussed and applied to the drift of the biological indicator Muggiaea atlantica in 1938. The two approaches agree to suggest that either method may be applied in biological distribution studies.

Some effects of drift, due to variable winds, on plankton distribution are outlined.

The circulation of the northern and north-eastern Celtic Sea, has been studied, using especially observations made in April 1950.

The Celtic Sea in that month was 0·5° C warmer than the average temperature 20 years earlier.

The following distinctive water masses have been recognized (i) Land's End water; (ii) South Wales coastal water; (iii) Carnsore corner current water; (iv) Nymphe Bank water, including a component enriched by up-welling off Waterford; (v) County Cork eddy water.

The South Wales coastal water, though rich in nutrients presumably derived from sewage effluents, was not very productive. A parallel is drawn with the Hyperion sewage scheme of the City of Los Angeles.

The low-salinity water present in the centre of St George's Channel in summer is attributed to flow from the coast of South Wales. In the autumn water is recruited more directly from the Celtic Sea.

The silicate content of the Carnsore corner current was half that in South Wales coastal water on the opposite side of the Channel.

Up-welling of water enriched by breakdown of bottom muds occurred off Waterford.

The drift system in the central Celtic Sea is dominated by the prevailing winds. The drift in April 1950 was a composite affair and it has been possible to dissect some of the components and to show how they interplay.

In about 7° W. long., a mixed water mass sets south from the Nymphe Bank and was identified for more than 100 miles.

A tentative explanation is offered for the distribution of compounds of phosphorus in terms of regeneration from bottom deposits.

Measurements have been made of the quantity and type of food assimilated by adult female Calanus helgolandicus (Claus) during the summer months.

Animals kept in the dark at 10° C under a continuous flow of ‘outside’ Plymouth sea water (0·95–2·50 mg insoluble organic material/1.) removed 26·0–66·5 μg/day/Calanus, of which 74–91% was actually digested.

Volumes of sea water filtered daily varied between 10·0 and 36·0 ml./ animal, with an average of 21·5.

The animals preferentially selected a diet of high organic content from the particulate food available, digesting average daily quantities of 18·1 μg carbohydrate, 6·5 μg lipid and 2·7 μg protein.

The average amount of food digested daily accounted for 25·3% of the dry weight and was equivalent to an average respiration rate of 26·5 μl. O2/ animal/day, which adequately accounts for the highest values reported by others for C. finmarchicus (Gunnerus) kept under similar conditions of light and temperature.

These results, which provide direct evidence that Calanus obtains the bulk of its food from particulate material present in the sea, have been discussed with especial reference to Pütter's hypothesis.

The accumulation of 134Cs and 42K from artificial sea water has been followed in crabs of the following species, viz. Carcinus maenas, Portunus puber, P. depurator, Polybius henslowi, Cancer pagurus and Corystes. cassivelaunm. In all cases 134Cs is taken up far more slowly than 42K but at equilibrium a higher concentration factor is attained by 134Cs. In Carcinus a value of about 8 is found for 134Cs and about 4 for 42K. Uptake of 134Cs in Carcinus is not affected by feeding on inactive food over a period of 1000 h. The relationship between the rates of uptake of the two isotopes is not the same in the different species and it is concluded that it would not be possible to predict with any accuracy rates of uptake for 134Cs in other species of crabs from the results of short 42K experiments.

Uptake of 134Cs was followed in the blood and tissues of Carcinus and Cancer, and muscle is the principal limiting factor in the attainment of equilibrium by whole animals. Uptake of 42K by tissues has also been followed and in all species nearly all the inactive K appears to be readily exchangeable. At equilibrium in all species plasma/sea water and tissue/plasma 134Cs ratios nearly always exceed those for inactive K. The tissue/plasma 134Cs ratios in Carcinus are about twice those for K and the significance of this has been discussed.

Loss of both isotopes in whole Carcinus is a slower process than uptake.Isotope accumulation takes place mainly across the body surface in unfed animals, but uptake of 134Cs from food is very rapid and complete and would considerably enhance the attainment of equilibrium in a natural environment.

Selective excretion of 134Cs relative to K has been found in Carcinus, Cancer and Portunus puber.

Polydora ciliata is a spionid polychaete found below mid-tidal level burrowing in a variety of rocks all of which contain calcium carbonate. It can also penetrate some non-calcareous materials such as rotten wood. It excavates a U-shaped burrow which it lines with a tube composed of mucoprotein and sand grains. This tube has a smooth inner lining of mucoprotein. Both food and tube-building material is collected by the palps and it is suggested that discrimination is made chiefly on size of the particle. Selection is made between the limits of 003-0-05 mm, the smaller particles passing down the gut whilst the larger are used in construction of the tube. A particle selection mechanism is suggested. The function of the segmental mucus glands is to provide the inner lining of the tube.

The problem of chemical penetration of rocks by animals is discussed. P. ciliata uses both mechanical and chemical methods. No acid has been identified, and the use of a sequestering or chelating agent linked with the biochemistry of mucus is suggested.

Tapeta were examined of light- and dark-adapted dogfish. Scyliorhinus canicula. The tapetum in the eye of this fish is fixed; pigment processes in the tapetum do not move when a fish is changed from dark to light and vice versa. A black ventral field and a bright dorsal fundus are always present.

Previous plankton work at Plymouth is reviewed briefly, and the limitations of the stramin ring trawl as a quantitative sampler discussed. The distribution of certain zooplankton ‘indicator’ species caught in hauls of the 2 and 1 m ring trawl during cruises in 1955 and 1957 is described in comparison with regular 2 m hauls taken throughout the same years at two stations near Plymouth.

The results support previous suggestions that ‘western’ water at Plymouth is derived from a region to the south of Ireland, i.e. from the north-west, and is not now in the direct path of the flow of water into the English Channel from the west.

An apparent northward spread of the warm-water copepod Euchaeta hebes during the past 50 years may be connected with the rise in sea temperature over the same period. It is suggested that related changes in distribution might be responsible in part for changes in the macroplankton community off Plymouth since the 1920's.

The salinity tolerance of herring 9-ca 24 cm in length was found to lie between 6‰0 and 40–45‰0.

Determinations of changes in weight and blood concentration (by measurement of the freezing-point), when herring were transferred from one salinity to another, demonstrated that extensive changes occurred in the blood. Under these conditions the herring experienced and survived blood concentrations equivalent to salinites of 13–22·5‰. A recovery to near normal (δ0·95 ≡ 15·8‰) took place in all the salinities within the tolerance range.

Badly descaled herring in sea water showed large increases in blood concentration before death.

A study of the kidney of the herring indicated that the ability to withstand the low salinities for long periods probably rested in the high glomerular count of the kidney.

The importance of damage to the skin for survival is discussed in relation to tagging experiments.

The results are also discussed in relation to the evolution of the herring.

Measurements of the ultra-violet absorption spectra between 200 and 400 mix, have been made with a spectrophotometer. At short wave-lengths natural sea water has double the absorbancy of artificial sea water. The difference in samples from shallow depths is ascribed to organic material, of which part may be the Gelbstoff of Kalle. Regional variations have been found, coastal waters having higher U.V. absorptions. A small seasonal effect with an increase in absorbancy in summer in the English Channel has been seen. In deep Atlantic water increased absorption below 235 m/x may be due to its high nitrate concentration. At longer wave-lengths absorbancies were less than in surface waters. Measurements of U.V. absorption may supplement other physical methods of characterizing water masses.

Details are given of the culture apparatus and methods found successful for the laboratory culture of species of Ectocarpus. In attempts to obtain uni-algal cultures of this genus several common methods were tried but only one of them, a modification of the plating technique, proved successful. Methods of washing and dilution were unsuccessful in giving bacteria-free cultures, presumably due to bacteria closely adhering to the cell walls. Ultraviolet irradiation was also unsuccessful but treatment with penicillin gave bacteria-free cultures of E. confervoides and E. secundus (Giffordia secunda).

The growth and nutrition of Ectocarpus confervoides has been studied in bacteria-free cultures. Growth was estimated by dry weights determined under controlled conditions. A method for inoculation of cultures of filamentous algae is described and a table of culture media is given. Following a lag of 5–7 days there was a period of growth, which was not truly exponential, extending over a period of 35 days. Calculation of the relative growth constant for the early stages of growth indicated that the alga doubled its dry weight every 6–7 days. Cultures of Ectocarpus remained viable for over 1 year in the light and for over 100 days in the dark. In natural sea-water media the maximum growth was brought about by the addition of 0·5 mM potassium nitrate and 0·1 mM potassium phosphate. Ferric chloride had no effect on growth but additions of manganese chloride did cause some stimulation. Additions of some complex organic mixtures slightly increased growth but Ectocarpus was unable to grow on a range of organic carbon source in the dark. The optimum salinity at 20° C was somewhat higher than that of natural sea water but was apparently lower at 15° C. The optimum pH was 8·0. Light intensities between 1350 and 16,000 lux had no marked effects on the growth rate but did effect the lag, the optimum for this being 7000 lux. Temperature also had no effect on the growth rate but did effect the lag. The optimum was 15–20° C but there was growth between 10 and 25° C. A considerable range of artificial sea waters, with and without organic additions was investigated, in no case did they give a yield greater than two-thirds that in natural seawater media. These results are discussed in relation to other workers findings.

The fauna of a muddy area in the northern North Sea (the Fladen ground) is compared with that of a similar area in a Scottish west-coast sea loch (Loch Nevis). These areas were selected because certain similarities in environmental features and in fauna, coupled with their marked difference in biomass, make them particularly suitable for studies of the factors affecting benthic production.

For macrobenthos samples (from a grab) a coarse sieve with round holes of 1-3 mm diameter and a fine sieve with meshes of 0-5 mm side were used. Meiobenthos samples (from a corer) were sieved through a 0124 mm mesh and the total residue stained in rose bengal.

The Fladen ground, depth 140 m, had annual bottom temperatures between 6-31 and 8-22 C and salinities between 35-20 and 35-2.50. The deposit was mainly of coarse silt with abundant tests of small Foraminifera. The fauna is redescribed. The characteristic species was the foraminifer Saccammina sphaerica. By separating empty tests from living specimens it is shown that this species was not so abundant as had been thought. The main lamellibranch was Thyasira equalis, not T. flexuosa as recorded in previous work. Other important species were the polychaetes Paraonis gracilis, Myriochele heeri, Spiophanes kroyeri, Tharyx sp., Lumbrineris impatiens, and Nephthys incisa. The standing crop of macrobenthos was 6-42 g/m2 wet weight.

The biometry of the Clyde population of long rough dabs has been studied and compared with the descriptions of the European race given by Norman in his monograph of the flat-fishes. The data consist of various body measurements together with the results of scale counts, fin ray counts and vertebral counts. The fin ray numbers fit into a pattern of increasing number with high latitudes when compared with other published data. There is a correlation between the number of anal and dorsal fin rays, and between these and the number of vertebrae. The variations that were found in the vertebrae of fifty-one fish are described. Only one sinistral long rough dab has been found out of 2357 specimens examined. From the British fishing statistics it is shown that the long rough dab is of little, and declining, commercial importance. In Canada, however, the American subspecies is becoming more important commercially.

Cod (Gadus morhua L.) from the Arcto-Norwegian stock that spawns off northern Norway were caught at various times during their gonadal maturation cycle over a period of 16 months. The ovaries were removed and either fixed for histological work or deep-frozen for the determination of vitamin A compounds.

The ovaries were inactive from June to September. Maturation began in late September-October and fully ripe eggs were present in February-March, the range of sizes being 500-650 /x. After spawning there was a period of resorption and regeneration, until May, followed by the quiescent summer period.

dry matter rose from about 16 to 29%; the total amount of vitamin A aldehyde, vitamin A esters and alcohol, carotenoids and lipids in the ovaries also increased, though the concentrations of the carotenoids and vitamin A esters + alcohol on a dry-matter basis fell. Vitamin A aldehyde was only found in maturing ovaries and in February, just before spawning, the weight ratio of aldehyde to esters + alcohol was about 10 to 1. The other substances were present in resting ovaries. The appearance of aldehyde in the ovaries occurred when there was histological evidence for the onset of vitellogenesis.

The numbers of fish eggs and planktonic stages of fish taken during a 5-year period by the Scottish research vessels in the northern North Sea have been associated with the presence of Sagitta elegans and S. setosa in the same collections and over an 11-year period with the presence or absence of S. elegans. The results confirm Russell's findings in the English Channel that fish larvae are more abundant when S. elegans is present than when S. setosa is present.

The total numbers of fish eggs do not show these differences; spawning does not appear to be any more productive in water associated with S. elegans, rather the reverse, and this is shown to be so for the eggs of those species separately examined. Numbers of the larvae were distinctly greater in the ‘mixed’ conditions indicated by the presence of S. elegans and a more abundant food supply is a possible cause. That the differences may signify a more fundamental effect, however, is suggested by the figures for cod and haddock eggs, which show the earliest stages to be more abundant where S. elegans was absent although later stages were more abundant when S. elegans was present.

Six naupliar and a cyprid stage for B. balanus are described and diagrams given for the general outlines and individual appendages. Sizes and setation formulae are given.

The naupliar stages resemble both B. balanoides and B. crenatus; attention is drawn to some distinguishing features and a key for the separation of the species is provided.

Forty-five specimens of Raia montagui Fowler were recently examined for their cestode parasites and twenty-seven of these contained Echeneibothrium maculatum Woodland, 1927, a species which has not been found in any other elasmobranch. In addition to its well-marked specificity to this host there is an indication that E. maculatum prefers to attach itself to a particular region of the intestine. The cestode was not recognized as a valid species by Baylis (1948) and is included as a synonym of E. dubium Van Beneden 1858 in the Plymouth Fauna List (Marine Biological Association, 1957), but Williams (1958a) and Euzet (1959) were not in agreement with these views. For this and other reasons a re-investigation of E. maculatum was undertaken.

Materials And Methods

The specimens of Raia montagui were trawled off Plymouth by R. V. ‘Sula’ during August and September, 1958 and 1959. The rays were kept alive in the large sea-water tanks outside the laboratory and were examined for their cestode parasites as soon as possible, usually within a period of 24 h. This was found to be necessary because elasmobranchs kept alive under these conditions, presumably without food, have shown a strong tendency to lose their intestinal parasites. It is hoped to discuss this phenomenon more fully elsewhere.

The intestines of some of the fishes were removed from the freshly killed hosts and opened with scissors following the course indicated by the arrowed broken lines in Text-figure 2. Having been opened in this manner they could be quickly examined as a flat piece of tissue for their cestode parasites (Text-fig. 3).

Yield of the supra-littoral chrysomonad Monochrysis lutheri varied directly as vitamin B12 concentration between the limits 0·1 and 100 μμg/ml., each μμg of vitamin supporting 0·55 × 106 cells. Between the same limits of concentration there was to be seen no significant deviation in initial rate of cell division from the mean value of 1·1 divisions per day (phototrophic growth: 2000 lux, 20° and 15° C), the conclusion being that limitation of the division rate does not occur before the concentration vitamin B12 has dropped below 0·1 μμg/ml.