of the Fishery Board for Scotland. 



83 



are active and pour a profuse gelatinous secretion into the spermatheca. 

 This fluid when treated with sea -water coagulates and turns white. 

 After fertilisation has taken place the vagina is found to be plugged, 

 a large white body effectually closing up the mouth of the spermatheca 

 and the vagina.* This body is much constricted at the mouth of 

 the spermatheca (fig. 6 ib.). It may be readily split longitudinally 

 into two halves (fig. 3). It is, without doubt, formed from the 

 secretion of the glands of the spermatheca . The fluid very probably 

 flows out into the vagina when the penis is introduced, and on 

 the withdrawal of the latter it solidifies and remains as a plug. This 

 plug is to be seen in all soft female crabs which have been fertilised, 

 with a few exceptions. Occasionally the plug is found in one vagina, 

 while it is absent from the other. Two male crabs were found which had 

 attached to their penes portions of the plug. In one case a crab o\-^, 

 which was still soft when obtained in October, had one of the halves of a 

 plug attached to the penis (fig. 8) ; while another, a crab of 5 inches, which 

 had been labelled (No. 826), had in November what appeared to be a small 

 portion of a plug on the base of the penis. The absence of the plug from 

 the vagina of the female may thus be accounted for. The plugs remain 

 some considerable time in the vagina, but disappear about the time the 

 crab becomes hard. Occasionally traces of the head of the plug are 

 apparently made out in the spermatheca. The vulva then closes, a 

 condition which is effected by its muscular structure. Up till this time, 

 and even later, the secretion remaining in the spermatheca has retained 

 a fluid consistency ; but it has nevertheless become more viscid, and of a 

 deeper amber colour. It eventually solidifies completely, and the 

 spermatheca shrinks. The mass of sperms, which shows very white 

 through the wall of the spermatheca, lies close to the opening of the 

 oviduct. Shortly after fertilization spermatophores are to be made out 

 in the spermatheca along with independent sperms and fat-globules, 

 which are evidently derived from the colourless fluid of the vas deferens. 

 The capsule of the spermatophore seems to rupture soon after it reaches 

 the spermatheca, for even before the crab has become hard the sperms 

 are all found to be free. When the spermatheca shrinks, it contains 

 the amber-coloured solid in its distal part (fig. 9 ib.), and just 

 inside the mouth, at the opening of the oviduct, are massed the sperms. 

 When the female extrudes her eggs, certain of the eggs are occasionally 

 left behind in the spermatheca, and they are to be seen in the amber 

 solid. In a female crab which has hatched its eggs, the solid substance 

 in the spermatheca is usually of two distinct kinds. It is very 

 probable that that is due to some of the ovarian fluid which is present 

 at the time the ovary is ripe lodging in the spermatheca and there 

 solidifying. 



Cano,t in referring to Milne Edwards' observation of the white plug 

 in the female edible crab, states that "it is no other than the remains 

 of the secretion which serves to glue the eggs at the moment of their 

 extrusion." Milne Edwards' supposition that the plug was the terminal 

 portion of the membranous penis of the male is of course quite 

 erroneous ; but Cano is also at fault in his explanation. 



It has been stated that the male crab after it has fertilized the soft 

 female retires to shelter in order to cast. Cano j says that, " in Decapod 

 Crustacea, coupling is always preceded by casting, first of the male, then 



* Present also in Carcinus mcenas. 



f Cano, "Morfologia dell' apparecchio sessuale femminile, glandole del cemento e 

 fecondazione nei Crostacei Decapodi." Mittheilungen aus der Zoologischen Station zu 

 Ne^el, Bd. IX., p. 510 Note, 1889-1891. 



% Ojp. cit., p. 530. 



