12 



Part III. — TivenUj-first Annual Report 



Megalops, which is a connecting link between the pelagic Zoea and 

 the demersal j^oung crab, which lives on the bottom, partaking of 

 the cliaracter of both, being adapted either for swimming or 

 crawling, and this finally gives rise to the young crab. 



With reference to growth, it was found that a considerable 

 amount of variation occurred, due to the fact that increase in size 

 only takes place after a moult, and the amount of the increase 

 varies not only with the individual, but also in the same specimen 

 in different moults. It is, however, possible with a fair amount of 

 certainty to separate the crabs into yearly groups if attention be 

 given, in the case of small crabs, to the month in which they are 

 captured. Observations have also been made on the amount of 

 growth that takes place in successive moults of specimens kept in 

 confinement; and Dr. Williamson's observations in this respect 

 were supplemented by a valuable series of cast shells from Mr. 

 H. T. Waddington, Bournemonth. The conclusions reached are 

 that the shore crab, when one year old, may measure from about 

 one-third of an inch to nine-tenths of an inch in breadth, the 

 average being a little over half-an-inch. When two years old the 

 average breadth of the male is about two inches, and of the female 

 nearly one inch and three-fifths ; when three years of age the male 

 is about two-and-two-fifths of an inch broad, and the female about 

 one-fifth of an inch less. The number of moults in a year was 

 found to vary considerably. 



The Invertebeate Fauna. 



The collections of Crustacea which have been made in the course 

 of the fishing investigations have proved of considerable interest, 

 and in the present Keport Dr. Thomas Scott contributes a further 

 paper dealing more particularly with the Copepoda. These minute 

 forms play an important role in connection with the food of fishes. 

 They exist in enormous multitudes and constitute one of the chief 

 agencies by which the primary source of food, namely plant- 

 organisms, is transformed and rendered available for the nutrition 

 of fishes. Many fishes, as the herring and the sprat, the anchovy, 

 the mackerel, and the pilchard or sardine, subsist mainly upon 

 copepoda, while almost all other fishes live upon them in their young 

 and early stages. 



In the present paper Dr. Scott describes a large number of species, 

 of which thirteen, belonging to eight genera, are new to science, 

 the descriptions being illustrated by a series of drawings. In some 

 instances the determination of these minute forms is of importance 

 for other reasons, as in tracing the course of sea-currents. Thus, 

 for example, one species which is described, Eucalanus crassus, was 

 obtained about ten miles off' Aberdeen, and was previously recorded 

 from the Moray Firth, from the region south-east of Fair Isle, and 

 from the Faroe Channel. Its distribution is known to extend as far 

 south as the Gulf of Guinea, and its appearance in the Moray Firth 

 and off the East Coast probably indicates the presence of Atlantic 

 water. It is interesting \i note that all the specimens were taken 

 in October and November. 



