356 MARKETABLE P.RITISII MARINE FISHES 



liquid or "white." The egg-shell remains even when the placenta is 

 formed. There are often three or four embryos in each oviduct, each 

 embryo having its own placenta. 



No placenta has been discovered in any family of rays, but on the 

 other hand the amount of nourishment supplied to the embryo in the 

 viviparous forms by the secretion of the walls of the oviduct is very 

 great. The gestation of several of the sting-rays and eagle-rays ( Try- 

 gonidiv and Myliobatida) of the Indian Ocean has recently been particu- 

 larly investigated by Professor Wood-Mason and Surgeon A. Alcock in 

 specimens obtained by the Indian Marine Survey steamer Investigator. 

 In Trygon Bleekeri the villi were found uniformly scattered over the 

 surface of the walls of the uterus or dilated oviduct. One specimen 

 examined was 3 feet across the pectoral fins, and contained an embryo 

 8 inches across. As there were no special organs for the absorption of 

 the uterine milk, as the secretion may be called, it was concluded that 

 it was taken through the mouth or spiracles and digested in the stomach. 

 This conclusion was confirmed by the very curious arrangement dis- 

 covered in another species of sting-ray called Pteroplatcea micritra. In 

 this case the villi were confined to the part of the uterus near the 

 spiracles of the foetus, and a bundle of very long villi actually passed 

 through each spiracle into the throat of the foetus, as seen in Fig. 157. 

 The spiracles were very large. These villi thus pour a nutritive secretion 

 into the throat of the foetus, much as the teat of a mammal pours out 

 milk, but without any sucking action on the part of the foetus. In 

 these cases the young, when ready for birth, is much larger and heavier 

 than the egg from which it arose. 



Many species of bony fishes also bring forth their young alive. 

 and in a fully developed condition, although this mode of propagation 

 is not exhibited by any of the commercially valuable species inhabiting 

 British seas. One small marine fish which is common on British shores 

 is viviparous, namely the viviparous blenny (Zoarces viviparus), and 

 there is only one other marine species occurring in Europe which has this 

 peculiarity, namely the so-called Norway haddock, Sebastes nonegicus. 

 These two belong to quite distinct families, the former to that of the 

 blennies, the latter to the Scorpaenidae, and there is no close similarity 

 between them in structure and habits. Zoarces is an elongated eel-like 

 form without scales, with short and flexible fin-rays, and with rudimentary 

 pelvic fins, while Sebastes is a much larger fish, of narrow compact shape 

 and with strong spines and scales. Zoarces haunts the shore and lurks 

 under stones, while Sebastes lives in deeper water and swims about 

 boldly. Both, however, are northern species, the Norway haddock 

 extending from Spitzbergen to the south-west coast of Norway, but 

 having rarely been taken on the more northern coasts of Britain, while 



