82 A NATURALIST ON DESERT ISLANDS. 



But the " suckling " period, if we may use such a term, 

 in the case of these rays, is got through prior to birth ; 

 just as in the case of certain nidifugous birds, the develop- 

 ment of the plumage is pushed forward in the egg, so that 

 when the chick is hatched it can run and fly and fend for 

 itself (cf. Megapodes). This process of " suckling," which 

 jjeems sb suggestively to foreshadow, thafc which should 

 be made perfected when mammals had begun their reign 

 on earth, is so interesting, that perhaps I may be pardoned 

 for again quoting Mr. Alcock (p. 210, loc. cit.). 



" Among them was a large female sting-ray, over nine- 

 and-a-half feet long. . . and lying unborn in her oviduct, 

 I found a young one, three feet in length. The mucus 

 membrane of the oviduct was shaggy, with vascular 

 filaments dripping with milk, and on microscopic examina- 

 tion I found that each filament was provided with 

 superficial muscles, whose contraction must serve to 

 squeeze the milk out. Some such mechanism is 

 undoubtedly necessary, seeing that the young one has no 

 power of extracting the secretion for itself. On examina- 

 tion of the young one, the mother's milk was found 

 inside the modified first pair of gill-clefts or spiracles 

 (the other gill-clefts being tightly closed), and also in large 

 clots within the spiral valve of the intestine, so that there 

 can be no doubt that in these viviparous rays the unborn 

 young one may be said to ' drink its mother's milk ' 

 like a mammal, even though the milk-like secretion 

 does not go in at the mouth, but by channels homologous 

 with the ear-drum of air-breathing vertebrates." 



