DEVELOPMENT 327 



below by the pectoral of the large male mate which was near 

 the big female. The embryo was well advanced, with a width 

 of more than three feet and a tail approximating eight feet in 

 length." It must be borne in mind that this extrusion took 

 place after the severe wounding of the mother fish, and may 

 not represent the normal process of birth. The embryos of 

 Saw-fishes (Pristis) are generally produced in fairly large 

 numbers, as many as twenty-three having been taken from a 

 female fifteen and a half feet in length caught oflf the coast of 

 Ceylon. The saw seems to remain more or less soft and flexible 

 until after birth, and the process of parturition is assisted by 

 the fact that the teeth along the margin of the saw at first 

 scarcely project through the membrane enveloping them. 



Among Bony Fishes viviparous forms are comparatively rare, 

 occurring only among the Cyprinodonts (Microcyprini) , the Surf- 

 fishes {Embiotocidae) of the North Pacific, the Blennies and their 

 allies {Blennioidea) and the Mail-cheeked Fishes (Scleroparei) . In 

 the Blennioids viviparous forms are found in three widely 

 separated families, but all the remaining members of the 

 suborder are oviparous. The specialised bHnd Cave-fishes, 

 both Cyprinodonts {Amblyopsidae) and Brotulids {Lucifuga, 

 Stygicola), are all viviparous. The eggs of Bony Fishes bringing 

 forth their young alive are fertilised while still either in ovisacs 

 in the walls of the ovaries or within the cavity of the ovary 

 itself, and may undergo their development in either position. 

 As usual, the embryos are nourished by the yolk contained 

 originally within the ova, but this may be supplemented, or 

 even to a large extent replaced, by certain nutritious secretions 

 from the walls of the ovaries or of the ovisacs, as in the Surf- 

 fishes, where this ovarian secretion is swallowed by the embryos 

 and absorbed by villi on the inner surface of their intestines. 

 The oxygen necessary for respiration is supplied by the blood 

 of the mother. 



The number of young produced at a single birth naturally 

 varies considerably. In the Surf-fishes (Embiotocidae) it varies 

 from three to forty or fifty; in most of the Cyprinodonts from 

 fifteen to twenty-five, although the Four-eyed Fish (Anableps) 

 may have only four or five; in the Viviparous Blenny or Eel 

 Pout [Z'^arces) of our own shores (Fig. 118) a female of seven or 

 eight inches in length produces twenty to forty young, one 

 from eight to ten inches, from fifty to one hundred and fifty, 

 while larger specimens have been found to contain more than 

 three hundred. It has been estimated that the Norway Haddock 



