APPENDIX I 361 



and ready for birth. When the young fish is born its fins and fin-rays 

 are completely developed, and it resembles its parent in everything 

 except size. 



In the curious Anabkps, a Cyprinodont of Guiana and Brazil, which 

 is distinguished by the interesting peculiarity that the upper half of its 

 eye is formed to see in the air, and the lower half to. see in the water, 

 the yolk is soon exhausted, and the nourishment of the embryo during 

 the greater part of gestation is provided by the nutritious albuminous 

 liquid secreted by the walls of the follicle. This liquid is absorbed by 

 papillae on the walls of the yolk-sac, which remains and enlarges after 

 the yolk has all been absorbed. The papillae are situated along the 

 course of the veins of this abdominal sac, and the nourishment they 

 absorb is thus taken up by the blood, and so supplies material for the 

 growth and development of the embryo. 



In the Embiotocidae of the Pacific coast, which appear to be known 

 in California as " surf-perches," the two ovaries in the female are united, 

 forming a single closed sac, the germinal folds in which the eggs are 

 produced depending lengthwise from the dorsal wall of the cavity and so 

 partially dividing it into several compartments. The embryos undergo 

 their development outside the follicles in which the eggs are produced, 

 lying between the folds of germinal tissue, which are abundantly 

 supplied with blood-vessels. There is very little yolk, and consequently 

 the embryos are nourished by a secretion of the walls of the ovary. At 

 an early stage, it is stated, the remains of the milt introduced into the 

 ovary in copulation are swallowed by the embryos. In later stages the 

 hinder part of the intestine is much enlarged and its inner surface is 

 provided with long processes (villi). The ovarian secretion appears to 

 . be swallowed by the embryo and absorbed by these villi of the dilated 

 hind-gut. Another peculiarity in these embryos is that the median fins 

 (dorsal, ventral, and tail-fin) are much developed, and their membranes 

 between the fin-rays are produced into thin delicate processes. Both 

 the fins and these processes are richly supplied with small blood-vessels, 

 and act the part of gills during the period of gestation, their function 

 being to absorb oxygen from the blood in the ovarian folds with which 

 they are in contact. This arrangement approaches somewhat to that 

 which exists in the placenta of mammals, but the relation of the embry- 

 onic structures to the maternal is much less intimate than in the latter, 

 and the function of the vascular membrane appears to be only respir- 

 atory, not nutritive. 



In the Embiotocidse the eggs are fertilised in the follicles in which 

 they are produced, but escape from these soon afterwards to develop in 

 the ovarian cavity. The ' ovary frequently contains forty or fifty young 

 Jfish, which at_birth measure 2 inches or more in length. 



