of the Fishery Board for Scotland. 



119 



The ovaries of these and of a number of other crabs were examined. So 

 far as could be made out, little difference exists between the process of 

 spawning in this form and in Cancer. 



TJie Formation of the Perivitelline Space in the Egrj. 



Ovarian Eggs. — A number of non-berried impregnated female crabs 

 (C. mamas) were examined in October, at a time when other individuals 

 of this species were spawning. They measured in greatest breadth ly 7 ^ in. 

 and upwards. Of these, some had orange ovaries containing eggs which 

 were practically ripe : others had pale, white, immature ovaries. The 

 two classes differed in external appearance. The shells of the crabs 

 which had orange ovaries were darker coloured than in the others. In the 

 former the thorax and third maxillipedes especially showed some brown 

 colour. In the crabs having immature ovaries the legs and thorax were 

 of a light green colour, which indicated that they had cast more recently 

 than the former (probably during the summer just past). 



The ripe egg, on being extruded, soon shows a perivitelline space. In 

 several instances when ovarian eggs, which were apparently ripe, were 

 put into sea-water a small separation of the chorion from the vitelline 

 membrane began to show itself, but although the eggs were kept in the 

 water till next day no large cr, in many cases, even distinct perivitelline 

 spaces developed, except in those eggs in which the inner (vitelline) 

 envelope had been ruptured, when large perivitelline spaces were rapidly 

 (in half-an-hour) formed. 



The formation of the perivitelline space would then appear to be due 

 to the osmosis set up through the chorion by the presence between the 

 chorion and the vitelline membrane of a fluid derived from the yolk. 

 The noivformation of the perivitelline space in the above-mentioned eggs 

 was possibly due to the fact that the complete ripening of the egg, viz. 

 with the occurrence of this fluid between the two envelopes, had not yet 

 succeeded. 



A few ripe eggs were found in the spent ovaries of certain berried 

 crabs. The spent ovary is a colourless empty sac, and shows here and 

 there usually one or two ripe orange-coloured eggs which have not been 

 extruded. In two cases examined none of the ovarian eggs showed a 

 perivitelline space, but on being transferred to sea-water the spaces 

 began to develop, and in a short time were large. In some cases the space 

 was distinctly reddish-coloured. It would therefore appear that a change 

 which makes the egg more favourable for osmosis takes place in the 

 ripening, probably just before extrusion. 



Spawned Eggs. — Some eggs which were taken by means of a brush 

 off the thorax of a spawning female were found to have a very slight 

 perivitelline space, but after they had been left in sea-water for a little 

 they showed large spaces. 



One female which was found spawning, or which had just finished that 

 process, had surrounding it a thick layer of eggs on the bottom of the 

 box. A small quantity of eggs only was attached to the endopodites. 

 The crab was transferred to a glass vessel, and in the course of that 

 operation a considerable quantity of eggs rolled off the abdomen. These 

 eggs showed large perivitelline spaces, and most had a peak -like eminence 

 on the exterior of the chorion. 



The eggs lying free on the bottom of the box round the crab also 

 showed large perivitelline spaces, but the little prominences were not seen 

 on the chorion. 



As was concluded in the case of Cancer, the perivitelline fluid is of 

 a sticky nature. 



