of the Fishery Board for Scotland. 113 



thus distended the ovary is swollen and contains a considerable quantity 

 of an amber-coloured albuminous fluid. In the dropsical ovarian egg the 

 perivitelline space is filled with an amber-coloured fluid, which is some- 

 wliat granular in appearance. Some of the eggs had been preserved in a 

 one per cent, solution of formaldehyde in sea-water, and the perivitelline 

 fluid was found to have solidified into a whitish substance resembling 

 coagulated albumen. This substance cut easily, being of a cheese-like 

 consistency, and it formed round the yolk-sphere a thick rind which 

 could be removed in two hollow hemispheres. The dropsical eggs when 

 fresh are rather dull in colour, in contrast to the bright normal egg. 



The ovarian eggs, and also those which are lying on the abdomen of 

 the crab before they become attached to the swimmerets, show under the 

 microscope no trace of cement on the outside ; the chorion shows a sharp 

 clean surface. If the ripe eggs be taken from the ovary and put into sea- 

 water a perivitelline space of more or less extent begins soon to appear. 

 The egg imbibes water, and the chorion or outer envelope is distended, 

 and stands out all round clear of the inner, the vitelline membrane [vide 

 fig. 95). 



Certain ripe eggs were extracted from the vagina of a female that had 

 been spawning, by means of a pipette introduced by the vulva. They 

 were practically identical with the ovarian egg, there being practically no 

 perivitelline space (fig. 94). 



If the eggs which have been extruded, and which are found in a semi- 

 fluid mass lying on the abdomen of the crab, be examined, some will be 

 found to be attached to the hairs, while others are loose. The latter show 

 large perivitelline spaces, but not so large as in the dropsical eggs. A 

 large quantity of eggs which had been extruded a week previously, and 

 which had not become attached, but were lying in a heap in a corner of 

 a box in which a spawning female was confined, had very large peri- 

 vitelline spaces ; they were stuck together, but were easily separated. 



The essential for the attachment of the egg to the hair of the 

 endopodite is the large perivitelline space, to which the great ductility 

 of the chorion contributes materially. In each of the eggs, from that 

 showing practically no perivitelline space, viz. the ovarian egg, to the 

 egg which has been a considerable time in water and in which the 

 perivitelline space has reached enormous dimensions (fig. 96), the chorion 

 always shows a sharp definite outline without wrinkles, i.e., as long as 

 the chorion is unpierced by the hair. 



Certain experiments bearing on the formation of the perivitelline 

 space were made on the eggs from apparently ripe ovaries during 

 November. A portion of the ovary was teased out in sea-water. It is 

 to be noted that the space does not begin to form in all cases — and even 

 if it does form it may be only slight in extent — although the eggs may be 

 indistinguishable from others which do so. Whenever the vitelline 

 membrane is ruptured (as may often happen in teasing the ovary), the 

 egg immediately forms a large perivitelline space, and the fluid in the 

 latter becomes amber-coloured or pinkish, whereas in the normal egg it is 

 colourless. 



On November 17 a female measuring 7|- inches across was dissected. 

 The ovary was friable, and the eggs, which measured "37 and "4 mm. in 

 diameter, separated out easily in water. There was no perivitelline 

 space visible. At the end of three minutes a distinct perivitelline space 

 had appeared. 



In another crab the ovary was full and of a crimson-red colour. 

 After being in sea-water for about an hour the eggs showed perivitelline 

 spaces of considerable amount. 



A crab measuring 7^ inches across on November 9th had an ovary 



H 



