ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 529 



In Scolopendra cingulata the nerve-cells are concentrated in ganglia 

 and are absent from the connectives. Sections show an external sheatli, 

 a lacunar or reticular tissue, nerve-cells, and central fibrils, as in lulus. 



e. Crustacea. 



Contributions to Life-History of Edible Crab.*— H. C. Williamson 

 has made a notable contribution to our knowledge of the life-history of 

 dancer pa gurus, as important practically as it is interesting theoretically. 

 A female capable of being fertilised is marked by the width of the 

 vagina and the size of the spermatheca ; but while a crab measuring 

 4\r in. acioss is capable of fertilisation, many crabs measuring 4|-5| in. 

 across are not fertilised. It is likely that the males copulate only with 

 females which have just cast the shell, while the new shell is pliable. 

 A crab does not always cast immediately after hatching ; it very often 

 carries eggs two years in succession ; this may depend on the store of 

 sperms in the spermatheca. The crab spawns offshore in deep water in 

 November, December, and January ; in summer it migrates to the warmer 

 water near the shore. The number of eggs carried increases with the 

 size of the crab from about half a million to three millions. In the 

 male maturity occurs at a somewhat less size than in the female. The 

 three external sexual characters, i.e. the differences in the abdominal 

 appendages, breadth of abdomen, and form of carapace, are discussed. 



In the small crabs of the beach there appears to be a slight 

 majority of females ; in the adult creel crabs the majority is on the 

 side of the males. The ecdysis is briefly described, and notice is 

 taken of the attendant physiological conditions. While the principal 

 time of casting is from July to September (both inclusive), casting takes 

 place during a large portion of the year, from May to November inclu- 

 sive. In the stage immediately preceding the adult condition, from 

 3-4 in. in breadth, the crab probably casts only once a year, but before 

 that oftener. The average ratio of growth on casting, perhaps -} to i of 

 the original size, has not been accurately determined. Regeneration of 

 the appendages takes place only when the crab is preparing to cast, and 

 the repair of injuries to the carapace takes place only at the same 

 period, or during the time the crab is soft. In adult crabs the new 

 limbs cannot reach the normal size until after at least two moults. The 

 rate of growth in crabs is subject to many irregularities. A probable 

 life-history is as follows : — The crab, hatched in inshore waters, reaches 

 a size of about an inch, passes into the beach group, grows to about 

 2^ in. across, leaves the beach for the littoral waters just below low- 

 water mark, grows to about 4 in., joins the mature group, and takes part 

 in the great seasonal migrations. But this summary gives only the 

 headings of a most interesting and valuable contribution. 



Otocyst of Decapod Crustacea, f — C. W. Prentiss has made an ex- 

 tended series of researches, histological and physiological, on this 

 subject. The material included adults and developing larvae of Macrura 

 (especially Palseomonetes) and Brachyura (Carcinus). Only some of the 

 most striking of his results can be mentioned. The thin chitinous 



'& 



* Eep. Fishery Board for Scotland, xviii. (1901) pp. 77-14:5 (4 pis.). 

 + Bull. Mus. Comp. Zool. Harvard, xxxvi. (1901) pp. 1G7-251 (10 pis.). Cf. ante, 

 pp. 515, 516. 



