222 THE INFANCY OF ANIMALS 



Later these external gills disappear, and the young is 

 nourished on a milky fluid formed within curious finger- 

 like outgrowths of the waU of its mother's womb, these 

 conveying the precious fluid to the gullet by thrusting 

 their free ends into a pair of large holes behind the head 

 known as spiracles — apertures which play an important 

 part in breathing during later life. 



That distinguished naturalist Colonel Alcock, to whom 

 we owe the discovery of the singular embryonic con- 

 ditions just described in the case of Pteroplatea, tells 

 us further, in his most delightful book " A Naturalist 

 in Indian Seas," that on one occasion when on board 

 the Investigator they caught a female of Dussumier's 

 shark measuring 7^ feet long. She contained ten 

 young ones when opened, and these, when turned into 

 a tub of sea-water, " swam about with perfect uncon- 

 cern." 



As a rule the number of young produced by viviparous 

 is far smaller than is the case with oviparous species. 

 Among fishes, however, this rule is subject to many ex- 

 ceptions. Thus the Blenny (Zoarces viviparus) produce 

 from twenty to three hundred or more at a birth, according 

 to the age and condition of the female ; while in the so- 

 called Norway haddock {Sebastes norvegicus) more than a 

 thousand are produced at a birth. 



That some fishes should be viviparous seems natural 

 enough, having regard to what obtains among the frog 

 tribe ; but one cannot suppress feelings of astonishment 

 at finding even one instance where hatching takes place 

 within the body of another animal ! This is actually so 

 in the case of a little fish known as the bitterling {Rhodeus 

 amarus), a small member of the carp family common in 

 parts of Europe, which enforces the hatching of its eggs 



