I 



APPENDIX I 359 



but they certainly leave the follicles and lie free in the cavity of the 

 ovary at a very early stage of development. Like the eggs of species 

 which are not viviparous, the eggs of Zoarces are contained in a spherical 

 egg-membrane, which when the development of the embryo has reached 

 a certain stage bursts, and sets the developing fish free in the ovarian 

 cavity. The eggs are thus hatched in the interior of the ovary, whereas 

 in other cases they are hatched in the sea after they have been expelled 

 from the parent fish. It has been estimated that this hatching takes 

 place about twenty days after fertilisation. After hatching the larvae 

 remain in the cavity of the ovary for a considerable time, and go through 

 the whole of their further development and transformation in this situa- 

 tion. The young, in fact, are not born until about four months after 

 fertilisation. In the Firth of P'orth females in which the young were on 

 the point of escaping were observed in February and March. The 

 newly born young are about' i^ inch long, and in all respects similar 

 to the parent in structure. It is thus clear that either a larger quantity 

 of yolk in the egg or some other supply of food must be available for the 

 larvie in the ovary of Zoarces to enable them to develop to this size and 

 condition, considering the imperfect condition of free fish-larvfe at the 

 moment when the yolk is all consumed. The explanation is that the 

 quantity of yolk is not large, but that the larvae are nourished also by an 

 albuminous liquid formed in the interior of the ovary as a secretion 

 from its walls. The number of young produced at a birth varies very 

 much in different females, and depends chiefly on the size of the latter. 

 Females of 7 or 8 inches in length are found to contain from 20 to 40 

 young, those of 8 to 10 inches from 50 to 150, while larger specimens 

 have been found to contain 300 young or even more. Some specimens 

 have been found in the gravid condition in summer and autumn, so that 

 there is reason to conclude that fertilisation takes place in some cases in 

 spring and birth in autumn, though it is by no means proved that the 

 same female breeds twice in a year. 



In Fig. 158 is shown the appearance of the developing egg of the 

 viviparous blenny before hatching, taken from the ovary on September 

 28th; it is magnified 12 times. Fig. 159 represents one of the young 

 nearly ready for birth, taken from the ovary on November 24th. The 

 little projection on the ventral surface beneath the pectoral fins is the 

 remains of the yolk-sac. The figure represents the young fish magnified 

 to twice its length. The little circle below represents the actual size of 

 the egg, and the line the actual length of the young fish at the stage 

 mentioned. The process of development and gestation in other vivip- 

 arous fishes is by no means exactly or closely similar to that which is 

 observed in the viviparous blenny. Great differences are found to exist 

 in the degree to which the nourishment of the embryo is derived from 



