of the Fishery Board for Scotland. 109 



pagurus, Carcinus ixvinas, Portunus sp., Hyas sp., etc., we will find the 

 eggs attached by their long stalks to the hairs of the eiidopodites. They 

 are closely set together, but in no case do we find two eggs stuck together. 

 If the eggs had been coated with cement, they could not have avoided 

 sticking together, and also to the exopodites. What special affinity can 

 there be betw^een the cement and the hair which does not exist between 

 the cement of two eggs 1 If the cement on being acted upon by sea- 

 water hardened, what is to prevent the two eggs from sticking together 1 

 When the eggs are extruded they lie in the incubatory chamber formed 

 by tlie curved abdomen in a semi-fluid mass, and they are there retained 

 by the overlapping exopodites. The latter prevent the eggs flowing out 

 over the edge of the abdomen. Now if each egg were coated with a layer 

 of cement, we should have the eggs concreted into a solid mass, and 

 while the endopodites would be imbedded in it, the exopodites would 

 be probably glued to the outside. The eggs never attach themselves to 

 the exopodites with which they are in close contact. 



No cement is supplied by the spermatheca. When the eggs are 

 extruded the spermatheca is dry except for the pasty white mass of 

 sperms; the solid remains of the spermatheca fluid are present. This 

 solid is the consolidated residue of the fluid which was secreted by the 

 spermatheca just after the crab cast and when it was impregnated. 

 Cano evidently supposed that the cement was secreted by the sperma- 

 theca. 



The egg does not derive a coating of cement from the ovary. The 

 ripe eggs, if taken out of the ovary, sometimes have a slight coating of an 

 albuminous substance ; it is derived from the yolk of ruptured eggs, 

 which is somewhat sticky, for by it an egg may become attached to the 

 bottom of the vessel in which it is ; but the union is of the slightest, and 

 a touch from a camel-hair brush is enough to dislodge the egg. That the 

 attachment does not result from an external coating of cement is there- 

 fore apparent. 



An opportunity which I had of observing the spawning of Cancer 

 pagurus has enabled me to describe the manner in which the attachment 

 of the eggs is effected. The fact that the eggs are attached to the hairs 

 of the endopodite, which are smooth, and not to the hairs of the 

 exopodite, which are plumose, necessitates a condition in which an attrac- 

 tion or affinity exists between the egg and the endopodite hair which does 

 not exist between it and the exopodite hair. 



The conditions which are necessary to the regular attachment of the 

 eggs to the hairs of the endopodite, and to them alone, are the following — 

 (1) the eggs themselves must not be coated with a fluid which is of itself 

 sufficient to cause it to adhere to anything when it is extruded, or other- 

 wise we should have the eggs adhering to one another ; (2) the hairs must 

 not likewise be coated with an adhesive cement, or they also would be 

 glued together ; (3) after extrusion a condition must arise which will lead 

 to the attachment of the eggs to the hairs of the pleopods, and the 

 relation is one which acts between each egg and some particular hair. 



The intimate relationship between the egg and the hair is due to the 

 hair acting as a skewer upon which the eggs are impaled and strung. 



On extrusion the ripe egg has two investing membranes, the outer or 

 chorion and the very delicate vitelline membrane, the " dotterhaut " 

 of Rathke. The hair perforates the chorion and enters the " perivitel- 

 line chamber," and passes out again without piercing the vitelline 

 membrane which is so closely applied to the yolk-sphere, and is more- 

 over so delicate that it is not readily recognised. The process is 

 more easily followed when the structure of the abdominal appendages is 

 examined. 



