SEA-FISHERIES LABORATORY. 459 



the endopodites of the pleopods secrete an adhesive fluid. 

 Williamson* gives a detailed explanation of the method 

 of attachment. He suggests that the endopoditic seta 

 penetrates the chorion of the egg in two places, and thus 

 the egg becomes skewered on the seta. The piercing of 

 the chorion liberates the adhesive perivitelline fluid, 

 which assists in making the attachment more permanent. 

 The chorion eventually becomes drawn out at the point of 

 attachment, and the egg appears to be attached to the seta 

 by a stalk (see fig. 80). 



According to Williamson, the number of eggs 

 attached to the abdomen may vary from half a million in 

 a small mature female to three millions in a large crab. 



Development. 



It is a surprising fact that the development of 

 Cancer jmgurus has never been satisfactorily investigated. 

 The internal changes do not appear to have been followed 

 in any Brachyurous embryos, and although the general 

 characters of the larval developments in the Brachyura 

 are well known, our knowledge of these stages in Cancer 

 pagurus is extremely scanty. 



The development may be divided into three stages- 

 embryonic, larval and post-larval. 



The embryonic development takes place while the 

 embryo is attached to the pleopods of the female, and, 

 therefore, extends over a period of about seven months. 

 The internal development during this period has not been 

 investigated, but it is very probable that the Brachyura 

 do not differ from the Macrura in this respect. The early 

 development has been thoroughly investigated in the 

 Macrura.t 



* Williamson. 23rd Report, Scotch Fishery Board. 



f SeeHerrick,F.H. "The Development of the American Lobster," 

 Johns Hopkins Univ. Circ, Vol. IX, 1890, No. 80. 



Keichenbach, H. " Studien zur Entwicklungsgeschichtc des 

 Flusskrebses," Ab. Senkenberg. Nat. Ges. Frankfurt, Bd. XIV, 1886. 



