of the Fishery Board for Scotland 



101 



outer envelope of the egg. The chorion of the egg is pierced by a hair 

 of the endopodite. The hair skewers the eggs on one after the other 

 until it is filled. 



Observations on the distribution of the edible crab, and additions to 

 the list of the labelled crabs which have been recaptured, are also 

 included in this paper. 



Impregnation. 



The act of impregnation is not very easily studied. It takes place 

 immediately after the female crab has cast. The conjunction of the male 

 with the female is so close, and at the same time so readily broken, that it 

 is not possible to follow the act completely by direct observation. The 

 study of the anatomy of the parts, however, enables one to understand the 

 operation in a satisfactory degree. While it is probably the case that in 

 the Brachyura impregnation takes place in a similar way in each species, 

 still the great variety in the form of the intromittent organ,* and also of 

 the vagina, of different species naturally infers a certain amount of 

 dissimilarity in the details of the operation. 



An attempt was made to observe the fertilisation in Cancer pagurus, but 

 actual coition was not seen. The female, which had just cast, was put in 

 beside a hard male crab. The female was so soft that it yielded to the 

 pressure of the fingers in every part. It lay a plump, almost inert mass 

 when it was withdrawn from the water. The male was in a box a little 

 more than 1 ft. cube. The female was introduced at the corner farthest 

 away from it. The female immediately made its way towards the male, 

 and when it came within reach of its chelae it remained perfectly still : 

 the male then gathered the female up with its legs and tucked her under- 

 neath him. Sometimes the female was right side up, at another she was 

 turned upside down beneath the male. In the case of Carcinus 7namas, 

 the male, on seizing hold of the female, immediately introduces its penes 

 into the vulvae. This did not happen in the case of Cancer pagurus. 

 This species appeared less at home in the boxes : the quantity of light 

 was probably too great. The male and the female were accustomed to lie 

 perfectly still. The former does not injure the female except by accident, 

 as for example when it is interfered with. The crab is extremely quick in 

 noticing a shadow cast on the water, and throws its chelae wildly about 

 to find the foe whose presence has been thus heralded. On one occasion, 

 when the two crabs had been separated in order to be examined, the male on 

 being released blindly striking out seized the chela of the female and 

 destroyed the limb. Impregnation was effected in the case of the crabs 

 (C. pagurus) in the Laboratory, but probably at night, as it was not 

 observed. 



The male sexual organ consists of three parts. First, the genital 

 papilla (fig. 47), which contains the external opening of the vas deferens, 

 v.d.; second and third, the appendages of the first and second abdominal 

 segments. Each of these organs is paired, so that there is a double male 

 organ, consisting of three parts. The female genital organs are also 

 paired. 



The genital papilla (g.p., figs. 39, 41, 47) is situated on the coxopodite 

 of the fifth pereiopod.f The vas deferens issues through a hole (e>., fig. 55a) 

 in the coxopodite, and is protected externally by the wide sac-like genital 

 papilla, the wall of which is strong though soft. The papilla is capable 

 of distension, and in the living crab is usually turgid. This condition 

 appears to be due to the introduction of fluid into the space surrounding 



* Brocchi. 



f Cf. Grobben and Brocchi. 



