108 



Part III. — Tv:enty-second Annual Report 



probably glandular. Some spermatophores were found on the plug inside 

 the spermatheca. In the vagina of the other side the short plug was 

 absent. 



A female which cast between the 22nd and 23rd October, and which 

 had not been in contact with a male, was dissected on the latter date. It 

 was already fairly hard, the integument resembling in feel stiffish brown 

 paper. The spermatheca was large, with thick walls; it had a little 

 white mass at its mouth. There was a certain amount of fluid in both 

 spermathecaB, but the latter were not globular. 



The Spawning of Cancer pagurus. 

 The Mode of Attachment of the Eggs to the Swimmerets. 



The external eggs of the edible crab are, like those of other decapod 

 Crustacea, carried, during incubation, on the hairs of the inner 

 branches of the swimmerets of the female. They are arranged on the 

 hairs from their bases to the tips as thickly as they can lie. When the 

 hair of a berried crab is examined, a condition similar to that shown in 

 fig. 21 is seen. The eggs are attached by independent stalks to the hair, 

 and they are moreover so closely set together that their stalks intertwine. 

 As, however, the egg is not always attached to one hair alone, but some- 

 times to two, we have the hairs grouped in bunches which correspond to 

 their whorl arrangement on the endopodite, e.g., cf. fig. 26. The inter- 

 twining of the stalks of eggs also tends to bind the hairs together. 



How do the eggs become attached so closely and regularly and in a 

 manner so economical of the space at their disposal 1 



Several agencies have been invoked to explain this. Cano* and 

 Herrickf have each given an historical resume of the theories held with 

 regard to the mode in which the attachment of the eggs to the pleopods 

 was brought about. It is not necessary to recapitulate it nor Cano's full 

 discussion of the egg-membranes of the decapods. According to Lere- 

 boulletj certain zoologists had explained the attachment of the ova to 

 an extension of the primary egg-membrane. 



There has, however, been general agreement that the fixation of the 

 egg is due to a cement with which it is coated ; that the egg becomes in 

 one way or another covered with a cement which on exposure to sea- 

 water hardens, after having glued the egg to the hair of a pleopod. 

 The cement was supposed to be derived from the ovary or oviduct by 

 Milne Edwards and Rathke ; from the spermatheca by Cavolini and 

 Cano,§ and in the case of Astacus from the integumental glands found 

 on the pleopods and ventrum of the abdomen by Lereboullet and Braun. 



While in the case of macrurous decapods this explanation might 

 not be dismissed on a priori grounds, it is impossible to accept it as 

 applicable to the Brachyura. It matters not how the cement is produced, 

 the question reduces itself to this position — Given an egg coated with a 

 cement strong enough to form the stalk of the egg, which resists rupture 

 for a period of eight or nine months, a period during which time the 

 swimmerets are being continually agitated in order to aerate the eggs, is 

 it at all likely that it would always attach itself to a hair, and never to 

 another egg similarly coated"? If we examine the eggs of«& Cancer 



* Cano, "Morfologia dell' apparecchio sessuale femminile, gland ole del cemento, e 

 fecondazione nei Crostacei Decapodi." Mittheil. Zool. Stat, zu Neapel, ix. Bd., 4 

 Heft., 1890. 



f "The American Lobster." Bull. U.S. Fish Commission for 1895, p. 127. 

 JHerrick, "The American Lobster." Bull. U.S. Fish Commission for 1896. 

 § Cano, op. cit. 



