Further tests on the settlement reactions of Ophelia bicornis larvae have shown that both Bullhill Bank and Salthouse Lake sands are less favourable to the larvae after sterilization than they are when fresh and untreated. The effect of a large variety of treatments of both sands has been investigated under conditions where the larvae were free to choose between two or more samples of sands presented together in the same dish. Results from these experiments, taken in conjunction with results obtained using conical vessels, show that sands may be classed as attractive, neutral or repellent with intermediate grading between these three main categories. It is concluded that organic material, living or dead, on the sand grains plays an important role in rendering a sand attractive or repellent to the larvae.

The anterior end of Arenicola contains an elaborately organized apparatus which has hitherto escaped accurate description, although it is of evident importance in the processes of extrusion and withdrawal of the proboscis, and exhibits striking variations within the genus as at present constituted. The ‘proboscis apparatus”, as it will be termed, includes the following components: (i) the proboscis itself and the first part of the oesophagus, together constituting the anterior portion of the gut; and (ii) the retractor sheath and gular membrane (“first septum” or ‘first diaphragm” of previous authors), both of which, in the writer's view, are derived from the first septum. Although of diverse morphological origin, these components are built together into a functionally unified whole. The purpose of the following paper is to give an account of the anatomy of the apparatus on which later studies of its mode of action can be based. The three species to be described, A. ecaudata Johnston, A. claparedii Levinsen and A. marina L., are chosen to represent the three sections into which the genus naturally falls. It will be shown that the proboscis apparatus undergoes characteristic structural modifications in each of the three, although its basal plan is always the same. So great are the divergences that probably each of them extrudes its proboscis in a different way.

An improved underwater photographic apparatus has been used to take further series of photographs of the sea bottom near Plymouth. The photographs in the present series are each ¼ m.2 in area instead of 1 m.2, and at this scale definition is much better.

Photographs of the bottom in the Rame Mud area showed ripple marks but no living epifaunal animals. In an area south of the Rame Mud, on a muddy sand and gravel bottom and in a similar area 6 miles south of Looe, dense populations of the brittle-star, Ophiothrix fragilis were photographed. In the area south of Looe this type of population (density more than 100 individuals per m.2) ha s been photographed on three different occasions in 1950–1. In a similar but still denser Ophiothrix population found ¾ mile north-west of Eddystone, there were about 340 individuals per m.2, and this aggregation was apparently of long standing, since exceptionally large dredge hauls of Ophiothrix were taken there in the last decade of the nineteenth century. It is suggested that the food supply for these populations, in the form of suspended material, is brought to them largely by the tidal streams and that the crowded beds are in localities where this is likely to happen.

Two experiments on the reaction to ultra-violet light of certain sound scatterers in the area are described.

The source was a 125 W. ultra-violet lamp.

The scatterers were detected using a Kelvin and Hughes recording echo-sounder, type 22.

The traces on both occasions were of the confused type caused by a number of different organisms, apparently lying between 20 and 60 m. and 8 and 30 m. respectively.

The responses of the different organisms to the ultra-violet light as shown by the components of the traces are described and their speeds of reaction calculated.

The types of organisms causing the traces are suggested.

Himanthalia elongata (=H. lorea (L.) Lyngb.), although a common brown seaweed on parts of the British coast, does not occur in sufficient quantities to render it of commercial importance. As a result, the work of Colin & Ricard (1930) appears to be the only investigation on the chemical composition of this species. Their material was collected in August 1929, but they give no indication of the size or condition of the plants which were analysed.

The presence of Trididemnum niveum (Giard) is reported from the Plymouth area. It is compared with the other two British species of Trididemnum, T. tenerum and T. alleni, with which it has in the past been somewhat confused, and all three are shown to be distinct species. A short diagnosis of the three species is given as an aid to identification.

Planktonic, benthic and littoral Crustacea were collected from localities around the British coast, from Norwegian and Faeroese waters and from the Antarctic, and their content of preformed vitamin A and carotenoid pigments was measured.

Methods are described for the preservation of specimens, the extraction and separation of vitamin A and carotenoids and the measurement of vitamin A by chemical, physical and biological tests, and of carotenoids by physical tests.

Free-swimming euphausiids were found to contain, in addition to large quantities of astaxanthin, high concentrations of preformed vitamin A, but no β-carotene.

There are few records in the literature of the relative proportions of the sexes in natural populations of echinoderms, and the samples studied have mostly been small. Selenka (1867) has stated that in Holothurians in general males are rarer than females, and Becher (1907) found that males were very rare in Rhabdomolgus ruber. Koehler (1907) noted that in the ophiuroidOphiacantha vivipara there were more females than males.

The respiratory rates of three species of planktonic copepods, Acartia clausi, Centropages hamatus and Temora longicornis, were measured at four different temperatures.

The relationship between respiratory rate and temperature was found to be similar to that previously found for Calanus, although the slope of the curves differed in the different species.

The observations on Centropages at 13 and 170 C. can be divided into two groups and it is suggested that the differences are due to the use of copepods from two different generations.

The relationship between the respiratory rates and lengths of Acartia and Centropages agreed very well with that previously found for other species. That for Temora was rather different: the difference is probably due to the distinct difference in the shape of the body of Temora from those of the other species.

The application of these measurements to estimates of the food requirements of the copepods is discussed.

Records were made of the presence or absence of food in the guts of Calanus finmarchicus caught in three different depths, at intervals of 4 hr. through 24 hr. It was found that 80-100 % of the Calanus caught at the surface were full of food at all hours of the day.

The number of Calanus containing food in deeper water was distinctly less. This may be correlated with the abundance of its food close to the surface. Diurnal vertical migrations took place on some occasions when samples were taken, but not on all.

In the absence of vertical migration Calanus was abundant at the surface and feeding continuously at all hours of the 24 hr. Where vertical migration took place feeding was mostly at the surface and was restricted to the hours of darkness, i.e. in summer to a period distinctly less than 8 hr. round midnight. Laboratory observations confirm the absence of any feeding rhythm.

This study was undertaken to increase our very incomplete knowledge of the annual cycle inascidians.

Berrill (1950) states that ‘the age of ascidians, with one exception, is practically impossible to estimate, unless a certain inhabited area is followed closely through seasons and years’. In the present work the method has been to follow certain aspects of the ascidian population of a chosen area for a period of nearly two years. The area was the Old Dock in Ardrossan Harbour, Ayrshire, and the ascidian population contained four species: Diplosoma listerianum (Milne Edwards), Ciona intestinalis (Linnacus), Ascidiella aspersa (Müller) and Botryllus schlosseri (Pallas). Diplosoma belongs to the order Enterogona, suborder Aplousobranchiata; Ciona and Ascidiella to the order Enterogona, suborder Phlebobranchiata; and Botryllus to the order Pleurogona, suborder Stolidobranchiata. Thus each of the three main suborders is represented, and the four ascidians studied are amongst the commonest British species.

Pandalus bonnieri is a dioecious species and no protandrous hermaphrodites have been seen.

The breeding season and incubation period for P. bonnieri are described.

The number of eggs laid increases with the size of the female. At 16 mm. carapace length the number of eggs is c. 1000 and at 24 mm. carapace length the number of eggs is c. 4000. The number for a single mm. size group varies roughly by ±10%.

Both male and female P. bonnieri become sexually mature at about 18 months, and in the Clyde seldom live beyond 3 years of age.

The colour of the eggs in P. bonnieri is sage green, in P. borealis blue green, in P. montagui light emerald green and in P. propinquus fawn.

Juvenile P. bonnieri can be separated into males and females by the shape of the pleopods within 4–6 months of hatching.

Records of nearly 2000 dogfish collected from the Ilfracombe region suggest that the spawning season of this fish starts in November and continues at least until July. This area probably represents a spawning ground into which the females migrate during the spawning season; the males follow them much later in April and May.

Figures are given to show the time taken at different temperatures for the embryo to develop to a series of definite morphological stages; these suggest that the temperature characteristic of the development (µ = 20,000) is substantially the same as for several teleost species.

The larva of the compound ascidian Polyclinum aurantium Milne Edwards (1842) has been described by Berrill (1950), and his figures and description indicate a dissociation between the ampullae and epidermal vesicles. A reexamination of the larvae of this form shows that this is a false disjunction. This is most evident in the younger stages. Berrill describes (p. 46) a ring of eight ampullae, in the larva of Polyclinum, surrounding the anterior tip of the trunk, and ‘numerous epidermal vesicles growing out or detached from two long strands reflected posteriorly” (p. 89).

It has been observed by Chu (1946) that the marine diatom Nitzschia closterium, in bacteria-free culture, grows in the light with inositol hexaphosphate as phosphorus source, and with glycerophosphate.

In the dorsal wall of the abdomen in the Paguridae muscle receptor organs have been found similar to those in the Macrura. In each of the first to fifth abdominal segments there are two receptor units on each side. A receptor unit consists of a long thread-like muscle, and a nerve cell connected with this muscle and sending its axon towards the central nervous system. The muscles of each pair run close together in the layer of the dorsal (extensor) muscles, but are independent from the latter following a more or less different course.

The nerve cells in each pair of muscle receptor organs are of two types. One of them has several very long distal processes expanding over one of the muscles. The other cell has one stout distal process giving off numerous but very short branches forming with their subdivisions a dense tuft of fibres terminating in the second muscle. The axons of the cells associate with one of the branches of motor nerves supplying the dorsal muscles and pass along these branches into the main nerve trunks of the respective segments.

Each receptor organ is supplied by several nerve fibres coming from the central nervous system.

Experiments have been made with the marine diatom Nitzschia closterium grown in artificial light with different nitrogen sources.

After the nitrogen source in the medium was exhausted, photosynthesis and cell division continued, the cells becoming nitrogen- and chlorophylldeficient.

On adding a nitrogen source to deficient cells and storing in darkness, synthesis of organic nitrogen, mostly water soluble, proceeded rapidly from ammonium, less rapidly from nitrate and very slowly from nitrite, with which it grows in light as rapidly as with nitrate or ammonium nitrogen.

Possible reasons why nitrate but not nitrite is reduced in the dark are discussed.

Chlorophyll and yellow pigments were synthesized in the dark by nitrogendeficient cells in quantity related to the organic nitrogen synthesized.

Chlorophyll was synthesized in small amount by non-deficient cells which had been growing rapidly before transfer to darkness. Cells contained less chlorophyll when grown in moderately bright than when grown in dim light.

There is still often confusion as to the identity of species of compound ascidians. This is due sometimes to a lack of published observations on the group, and sometimes to seasonal variations from the described condition. An attempt has been made to follow the growth and variation of the species in the Plymouth area throughout the year. During the course of these investigations all the species of the sub-order Aplousobranchia formerly recorded from this area were encountered, with the one exception of Distaplia garstangi Berrill. In addition, two new species were taken: a species of Polycitor, the first record of the genus in these waters, and a species of Lissoclinum.

During my stay at the Plymouth Laboratory in 1931 I had an opportunity of investigating the innervation of the heart of Ligia oceanica, and of making some experiments on the function of the ganglionic trunk which constitutes the main element of its innervation. In a short note describing these experiments (Alexandrowicz, 1931) it was stated that a description of the arrangement of the nerve elements would appear in a short time. However, on later examination of the preparations it seemed to be desirable to verify some of the findings, but the same animal was no longer available. Another isopod, Mesidotea entomon, with which I tried to continue the work during my visit to the Marine Biological Laboratory in Hel, proved to be much less suitable for this kind of investigation despite its larger size. Later events, unfavourable for scientific work, caused the loss of all my preparations and a further delay. It is only now, thanks to the chance of working again at the Plymouth Laboratory, that I have been able to resume my investigations.

The fifth paper of this series (1930) was the author's last, after which the work was handed over to L. H. N. Cooper. It was resumed by the author in 1948 to compare the early years with the post-war, since the determinations had lapsed. Measurements of the extinction coefficient of the water were also resumed, and it was desirable to obtain the chemical data at precisely the same time.

The phosphate results are, as before, expressed as P2O5 in mg./m.3, since for crop calculations this old unit is convenient; to convert to mg. P, which is more rational, multiply by 0437; to bring to milligram atoms multiply by 0–0141. The analyses have not been corrected for salt error, since the early results were not^ and the factor for this correction has not as yet been agreed upon.

The silicate results are given as mg./m.3, of SiO2, but though the standard used in Plymouth was checked for me by Dr E. J. King in Canada and agreed with his (King & Lucas, 1928), yet a different value had to be assigned to the silica factor of the picric acid solution. All values have accordingly been multiplied by I.44.

The phosphate results for E1, surface, from 11 February 1948 to 1 February 1949 are shown in Fig. plotted against the dates.