The following is a detailed account of the results of my investigations concerning the breeding and the development, under natural and artificial conditions, of some of the fishes met with at Plymouth. These researches extended over the period from the beginning of August, 1887, to the end of August, 1888. I have given brief preliminary accounts of some of the results in No. II of the ‘Journal,’ issued in August, 1888. As I mentioned there, the laboratory work was carried on from August to November in a small room hired for the purpose near the fish quay; from November to June, 1888, in a single room in the Laboratory without a constant supply of sea-water; after that time the Laboratory being finished all its appliances were available.

Regeneration of ectoderm and mesogloea, and the interactions of these layers, in the sea anemone Calliactis parasitica (Couch) have been studied by examining the healing of simple wounds. Studies included the part played by the mesogloeal cells, the origin and functions of which have been much debated.

The presence of two dinoflagellate species of the genus Asterodinium, which are a priori representative of warm waters, is reported for the first time in the western Mediterranean Sea. Asterodinium libanum was identified in the Bay of Villefranche-sur-Mer (Ligurian Sea), while Asterodinium gracile is reported in the Tyrrhenian Sea. These findings are discussed in the context of the progressive warming of Mediterranean waters.

Morphometric and gonad maturity of Libinia spinosa on the coast of Mar del Plata, Argentina, were assessed. In both sexes various morphometric features were measured to determine the morphometric maturity, and through macroscopic inspection of gonads and analysis of its content, different stages of gonad maturity were described and the physiological maturity was estimated. In females, the carapace width ranged from 8 to 56.5 mm while in males from 4.6 to 81.97 mm. The size at which 50% of females were morphometrically mature was calculated at 40.6 mm. Based on the allometric growth of the abdomen, two morphometric groups of females were recognized as juvenile and adult phases. In males, results of principal component analysis showed that the most suitable variables that efficiently represent the size and sexual differentiation factor were the carapace width and cheliped length respectively. The size at which 50% of males were morphometrically mature was estimated at 58.9 mm. Based on the allometry of the cheliped growth, two morphometric groups were recognized as immature and mature phases. Males maintained under laboratory conditions moulted and growth was related to regular and terminal moults. Males reached their terminal moult at a wide size-range, from 48.5 mm to 61.4 mm of carapace width. This terminal moult coincided with the size of morphometric maturity. In both sexes four stages of gonad development were described, two corresponded to immature phases and two to mature phases. The size at which 50% of females and males reached gonad maturity was LC50 = 40.33 mm and LC50 = 33.6 mm, respectively. In females, both morphometric and gonad maturity occurred at a similar size. In males, gonad maturity is acquired prior to morphometric maturity, thus three different types of males were characterized: (1) those with small carapace width and cheliped, without spermatophores in their vas deferens; (2) those with large carapace width and small cheliped, bearing spermatophores in their vas deferens; and (3) those with large carapace width and cheliped, bearing spermatophores in their vas deferens.

A study was made ofGeryon trispinosus (Herbst) from the Porcupine Seabight in the north-east Atlantic, based on detailed examination of 687 specimens, and carapace length data for a further 2000. Evidence indicates that males become sexually mature at 30–35 mm carapace length, and females between 12 and 15 mm. There is probably a terminal anecdysis, in males at 55–65 mm and in females at 45–50 mm. The chelae show limited heterochely and marked right-handedness in both sexes. Relative growth in chelae and abdomen followed expected patterns, except that the right chelae of males decreased in relative size at the puberty moult. Seasonal reproduction is indicated: laying in September/October, hatching the following May, and settlement from the plankton in August/September.

The well-known work of Hensen (1887) was the first serious attempt to determine the actual number of individual plankton organisms in sea-water. Hensen's method consisted in straining a vertical column of water through a net of fine-meshed bolting silk having 6,000 to 6,500 meshes per square centimetre, the average length of the side of a mesh being 50 µ. A carefully measured sample of the organisms retained by the net was taken and the number of organisms in it counted. From this, since the area of the mouth of the net and the distance through which it was drawn were known, the number of organisms in a unit volume (1 litre) of water could be calculated, with the help of a coefficient of filtration for the particular pattern of net employed, which was determined experimentally. Many small organisms, however, escaped through the meshes of the net, and Lohmann (1902, 1908) made a special study of these by filtering through hard filter paper or closely woven taffeta silk, by an examination of the filtering apparatus in the “houses” of Appendicularians, and finally, for the quantitative estimation of the smallest organisms of all, by subjecting samples of sea-water to the action of a centrifuge making 1,400 revolutions per minute for a period of 7 minutes. The use of the centrifuge has been continued by Gran (1915) and by Lebour (1917). For the full literature of the subject the reader is referred to Gran (1915) and Lohmann (1911).In the course of my work on the cultivation of plankton diatoms (1910, 1911) I became convinced that even the quantitative method based on the use of the centrifuge fell very far short of giving the total number of organisms actually present in a sample of sea-water, and the results recorded in the present paper show that this is certainly the case.

1. The present paper deals with changes of biomass and size of Calanus finmarchious throughout the year the Plymouth area.

2. The material was supplied by regular oblique hauls during 1930; Stage V and adult males and females having been examined. Calanus finmarchicus occurred throughout the year reaching its maximum value in May, being abundant from the middle of April to the middle of September.

The benthic fauna of a fly-ash dumping ground off the Northumberland coast has been studied in comparison with that of the surrounding natural sediments and a designated offshore spoil ground. Continued ash dumping has resulted in an increase in the silt fraction of the sediments, together with the appearance of pozzolanic aggregates at the sites of greatest dumping, some 3·5 km offshore. The sediments here show a more rapid decline in Eh values with depth. The natural benthic macrofauna represented a typical Echinocardium-filiformis community, giving way throughout the offshore spoil ground to a ‘ Paraonis-Magelona’ community dominated by smaller polychaete species more tolerant of poor sediments, while the stations at the centre of the ash dumping showed an anomalous community structure. The density of the fauna was reduced at the centre of the ash dumping, the worst station yielding only eight individuals in 0·2m. Contours of numbers of macrofaunal individuals and species, of faunistic diversity and biomass, and of meiofaunal numbers all show a similar pattern of some depression along the spoil ground, and greater depression at the ash-dumping centre. Statistical analyses confirm a significant negative correlation between faunistic parameters and ash content. Deposit-feeding species represented a lower proportion of the community at sites of high ash content. The negative correlation between faunistic diversity and ash content was statistically significant over an area of 43 km around the centre of the dumping. The faunistic impoverishment is considered mainly to be a response to the dumping per se, and options for reducing this effect are discussed.

Profound cyclical changes were observed in the epidermal thickness and in the concentrations of goblet cells and epidermal melanophores in an inshore population of winter flounder, Pseudopleuronectes americanus Walbaum. There is sexual dimorphism which is particularly prominent in the thickness of the epidermis during the pre-spawning period in the spring. At this time the male develops a significantly thicker lower epidermis. During and shortly after the spawning period (lower skin), or somewhat earlier (upper skin), there is a significant thinning of the epidermis in both sexes. Significant increases occur in goblet cell frequency, those of females being greater than males, during autumn and early winter and the April/May pre-spawning period. Goblet cell frequencies decrease in mid-winter (January–March) when general activity is low, and in the thin summer epidermis. These observations are compared with data from other teleosts and discussed in relation to hormones possibly affecting the epidermal structure of teleosts and in relation to known hormonal cycles in winter flounder.

Ilyanassa obsoleta (Mollusca: Gastropoda) is an abundant inhabitant of salt marshes and tidal flats on the east coast of North America. Populations of this snail may be heavily infected by larval trematodes. Three species were observed in this work, Himasthla quissetensis, Lepocreadium setiferoides, and Zoogonus rubellus. Mostly as single-species infections, all occupy snail tissues as parthenitae that produce cercariae, which are released from the snail to infect the next host. By periodically testing snails for cercarial emission, single-species infections are here shown to persist over six summers and double-species infections are also noted to be long-lived. Among the 32 snails followed, 25 released the same (or no) cercariae throughout observation periods averaging three years. The other seven indicated infection changes, but only two of these are judged to reflect actual changes. The probability that a snail changed infection status in this study is thus 2.1% y−1. Ilyanassa obsoleta individuals, and apparently their trematode infections, can persist for decades. Because species colonize and get evicted infrequently, sets of trematode species infecting I. obsoleta individuals (infracommunities) are concluded to be isolationist in character.

A study has been made of the relationship of Phaeodactylum tricornutum (Bohlin) to iron, manganese and zinc. Evidence is presented showing that, in batch culture, the three elements behave differently as regards their uptake into the cells, the amounts present in the cells and their distribution between cells during the growth of the culture. The implications of these differences are considered.

In the common intertidal sea anemone Actinia equina (Cnidaria: Actiniaria) the morphological plasticity and lack of hard parts has caused considerable debate as to what constitutes a species. Over the last several years genetic studies have indicated that this ‘species’ consists of various separate gene-pools which appear to function as cryptic biological species. Conventional taxonomy has often concentrated on the use of a cnidome, the type, structure and number of nematocysts ('stinging’ cells). However, the usefulness of nematocysts to distinguish among various morphs of A. equina and other anthozoan species has recently been questioned. Here we describe the first detailed study of nematocyst differences between two well characterized genetically differentiated morphs with different coloured pedal discs. Measurements were taken from each type of nematocyst in five different tissues. Contrary to expectations, clear and significant nematocyst differences were found between Actinia with red or pink pedal discs and others with green to grey pedal discs. These findings support previous electrophoretic studies and suggest that quantitative descriptions of the cnidome may accurately identify separate species within other genera of Anthozoa.

The chromosomes of Platynereis dumerilii (Audouin & Milne-Edwards) are described here for the first time. A modal chromosome number of 2n=28 was recorded, based on counts conducted on metaphase spreads prepared from 24-h-old larvae. The karyotype comprises seven pairs, each of relatively large median (arm ratio, p/q=l.00–0.59) and submedian (arm ratio, 0.59–0.33) chromosomes. Attempts were also made to band the chromosomes using C-banding and silver staining methods. C-band-positive regions were localized on four chromosome pairs (three median, one submedian). A further two chromosome pairs (both median) were observed to have terminal nucleolar organizer regions (NORs). To our knowledge, this is the first time that these banding methods have been successfully applied to any polychaete species. These results are discussed in relation to the karyotypic variation within the class Polychaeta, and the family Nereidae in particular. A stable karyotype consisting of a moderate number of large and morphologically well-differentiated chromosomes, coupled with the ease of culture under laboratory conditions and short generation time, suggests that P. dumerilii is a potentially suitable model for evaluating marine contaminants for genotoxic activity.

Stomach contents of six striped dolphins taken as by-catch in the swordfish fishery in the eastern Mediterranean Sea off the Turkish coast were examined. In total, 29 taxa were identified to species or family and 1777 individual food items (1394 bony fishes, 289 cephalopods, 94 crustaceans) were counted. Diaphus spp. and Ceratoscopelus maderensis were the most remarkable ones, as they accounted for 70.45% of the total number of fishes. Onychoteuthis banksii, on the other hand, was the only cephalopod species found in all stomach content analyses and represented 38.06% of the total number of cephalopods. Bony fish species: Myctophum punctatum, Notoscopelus elongatus, Electrona risso, Sudis hyalina, Moridae sp., Phycidae sp., Sternoptychidae sp. and cephalopods: Pterygioteuthis giardi and Chtenopteryx sicula were reported the first time in the stomach contents of striped dolphin in the Mediterranean Sea.

The tidal rhythm of migration of the mud-fiat diatom community is a curtailed diurnal rhythm. Evidence is given of the similarity of these two oscillations in the laboratory and in the natural conditions of the estuary. However, the interference of the diurnal rhythm by water or stirring results only in one repeated rhythm on the following day; thereafter the migrations revert to a day-length-induced synchronization.

Samples of phytoplankton from nets towed in the surface waters off Plymouth over a period of 24 years were subjected to a correspondence analysis. There was a high species diversity throughout the year, and a strong seasonal cycle. A total of 104 species was divided into eight groups showing different seasonal and year-to-year occurrence. Over the 24 years the seasonal pattern of species changed in a fairly systematic way and there were two periods (1968–70 and 1983–85) when the changes were most marked. These patterns could be related to changes in the weather patterns, and were similar to those found by other workers in other groups of organisms and in other areas.

The pronounced Bohr shift of cephalopod haemocyanin may be related to the formation of octopine, rather than lactate, by cephalopod muscle. Octopine is a much weaker acid than lactate.A highly pH-sensitive oxygen binding curve would permit the efficient unloading of oxygen at the tissues even for a moderately small decrease in venous pH.

The free-running locomotor activity rhythms of freshly-captured swimming crabs Liocarcinus holsatus and L. depurator have been studied in constant conditions in the laboratory. L. holsatus captured in the intertidal zone of sandy beaches showed strong circatidal activity rhythms with maximum activity at high tide. L. holsatus captured in the sublittoral zone had a clear tendency to show circadian activity rhythms with highest activity during day-time hours. L. depurator occurred only sublittorally and showed circadian activity patterns with highest activity during the night. Exposure to hydrostatic pressure cycles of tidal amplitude and periodicity, entrained strong circatidal activity rhythms in previously arhythmic L. holsatus. This activity pattern also showed a marked circadian component. Exposure to the same regime entrained a circadian rhythm, but not a circatidal rhythm in L. depurator. In the sublittoral zone L. depurator is active mainly during the night, whereas L. holsatus, is active mainly during the day. This may constitute a behavioural mechanism for minimizing competitive interactions between these two sympatric crabs.

Tolerance and behaviour to hypoxia and anoxia by the annelid Loimia medusa (Savigny) (Polychaeta: Terebellidae), a common species in estuarine habitats where summer hypoxic events often occur, were examined in the laboratory. The worm can tolerate anoxia or severe hypoxia (7% air saturation at 26°C) for 3 to 5 d. Under low dissolved oxygen (<14% air saturation) feeding stops, although tube irrigation continues and periodic protrusions from the tube are common. Most worms come out to the sediment surface, but the number of worms dead on the surface is higher in anoxia than in hypoxia. The prevalence of L. medusa in deep estuarine channels may be partially explained by its tolerance to prolonged periods of hypoxia (14 d at 14% air saturation). Our data, however, suggest that subtle changes in oxygen concentrations may be important in the control of populations of L. medusa in habitats affected by low oxygen disturbances.

This paper presents baseline information on maternal behaviour and lactation in the Mediterranean monk seal, with particular focus on the age at which pups are weaned. The study was conducted in the western Saharan population, the only surviving colony of the species. The first moult finished at a mean pup age of 72.3±17 d (N=17) and, in contrast to other taxonomically-related phocids, this process was not associated with weaning. Lactation lasted a mean of 119.4 d (N=9; range: 103–149 d) in the pups that could be monitored until full weaning had taken place. This period almost doubles the maximum lactation length reported in other phocid species. During the first week after birth the mother–pup bond was well developed and mothers always remained with their pups. The time invested in nursing (17%, SD: ±36) and in mother–pup interactions (14%, SD: ±32) was higher during this period than afterwards (8%, SD: ±23 and 4%, SD: ±19, respectively). After the first week, nursing continued but mothers started to leave their pups in order to feed at sea. Weaning occurred gradually. Already since birth, pups were active and mobile, and swam frequently before moulting or weaning occurred. Fostering and milk stealing were common patterns of behaviour for both lactating females and pups. In 26.6% of the suckling episodes observed in mother–pup pairs of known identity, pups suckled from females other than their mothers. Some females nursed more than one pup, at least occasionally, and in some cases a pup was fostered long-term by an alien female. The Mediterranean monk seal exhibits maternal-care characteristics that are more like otarids than phocids. This observation contradicts previous proposals that a short lactation period is a phylogenetic characteristic of phocids. Several of the unusual maternal traits observed may be favoured by year-round access to abundant food supply, availability of breeding sites, and mild climatic conditions. This information should be taken into account when designing conservation strategies for the species and, very particularly, in the implementation of pup rehabilitation programmes.