of the Fishery Board for Scotland. 



97 



The Matter e Male Crab. 



The male crab is ripe at a somewhat less size than the female. The 

 condition of maturity in the male is the presence of ripe male elements 

 in the vas deferens. The sperms of the edible crab are not unlike those 

 of Carcinus mamas, as described by Grobben*. They are disc-shaped 

 when seen from above ; in the centre appears a small refractile body 

 containing a nucleus; the periphery of the disc is transparent and 

 delicate. (Fig. 11, a, Plate I.) When seen from the side the sperm 

 is seen to be spindle-shaped. (Fig. 11, b, ib.) In contradistinction 

 to those of Carcinus, the edge of the disc is smooth, not serrated. 

 The sperms are not found free in the vas deferens, but are packed 

 in capsules — sperm atophores. The opening of the vas deferens to 

 the exterior is on the apex of a membranous papilla situated 

 on the first joint, coxopodite, of the last thoracic limb (op. Brocchit). 

 The presence, then, of spermatophores in the vas deferens is the 

 character of a ripe male. They are to be found in crabs as small 

 as 3| inches across the back. In crabs of this size, and certain others 

 up to 4i inches, the vas deferens is of small diameter, colourless and 

 tense as a crystalline rod. It encloses a colourless fluid, which consists 

 essentially of minute fatty corpuscles, with a few spermatophores. 

 Between 3|-4|- inches most of the crabs exhibit vasa deferentia of this 

 description. Above 4-1- inches, however, the vas deferens is white, the 

 colour being due to the great numbers of spermatophores which it con- 

 tains. A still further stage of development is seen in the extraordi- 

 narily swollen condition of the sperm-duct in most adult hard crabs. 

 (In all conditions of the vas deferens the colourless fluid containing the 

 fat corpuscles is present also.) In the adult male, when the swollen 

 vas deferens is torn, the contents flow out profusely through the con- 

 traction of the muscular wall of the duct ; and if the membranous genital 

 papilla is pressed, spermatophores are expelled. It is very probable 

 that this swollen turgid condition will materially aid, if it is not neces- 

 sary for, the act of fertilisation. The vas deferens of a very soft male 

 crab is of small diameter, though white in colour. In such a case no 

 spermatophores may be extruded in response to pressure of the papilla. 

 As the crab hardens, however, the diameter of the sperm-duct increases 

 greatly, and there is conclusive proof that a male crab, even before it 

 becomes quite hard, may fertilise a female (vide above — Fertilisation, 

 p, 83). In hard crabssmaller than 3^ inches across no spermatophores were 

 made out, and in six hard crabs, measuring from 3| to 4|- inches, none 

 were noticed. (Vide Table III., p. 98.) Seventeen hard crabs, from 3| to 

 4|- inches, showed colourless vasa deferentia containing spermatophores ; 

 six between these limits had white sperm-ducts ; above 4^ inches all 

 hard crabs had white and swollen vasa deferentia. All male crabs, 

 then, above 4-L inches are probably mature. In the case of the female 

 crab, the observations made so far indicated 4-L inches as the smallest 

 size of maturity. Certain male crabs are, however, mature at a smaller 

 size. 



In Table III. the description is given of the condition of the vas 

 deferens in 124 crabs. These observations cover the period from May 

 to December inclusive. I, however, have no doubt that the male crab 

 is ripe during the whole year, the only event which will interfere with 

 its reproductive activity being casting. 



The smallest ripe male observed by Wilson^ was 5 inches across. 



*"Beitrage zur Kenntniss der mannlichen Geschlechtsorgane der Dekapoden," 

 Arbeiten aus dem Zcologischen Institut der Universitcit, Wien., T. i., 1878. 



f "Recherches sur les organes genitaux males des Criistaces decapodes," Annales 

 des Sciences Naturelles, Zoologie et Paleontologie, T. ii., 1875. 



%0p. cit., p. 7. 



