138 CHILDHOOD OF ANIMALS 



pharynx, a very singular case of the subordination of the normal 

 appetite to an unselfish duty. In the cichlids the same habit has 

 been developed, but most usually by the females. In Aspredo, a 

 large fish found in Guiana, there is a still more remarkable mode of 

 brood protection. The skin of the under surface of the body, over 

 the head, abdomen and paired fins becomes soft and spongy, and 

 the eggs adhere to this in a single layer ; whilst the skin of the 

 mother forms cup-shaped receptacles richly supplied with blood- 

 vessels, and suggesting that the young embryos obtain nourishment 

 by a kind of placental connection. In the small fresh- water 

 bitterling of Europe, the female develops a very long tube at the 

 end of which is the orifice by which the eggs leave the body. She 

 uses this as an ovipositor, inserting it between the valves of the 

 shells of fresh-water mussels and discharging the eggs into the 

 branchial cavities of these animals, within which they go through 

 their development in security. 



In nearly all the bony fish the eggs are fertilised after they have 

 left the body of the mother, and their subsequent development, 

 whether they are turned adrift or guarded in some of the curious 

 ways I have mentioned, is really independent of her. But in a 

 few instances not only is there internal fertilisation, but a large 

 part of the development takes place in the ovary of the mother, 

 and the young larvae are fed not only by the small amount of yolk 

 deposited in the egg, but by a secretion from the walls of the 

 ovary which they swallow and digest. The blenny is the best- 

 known case of this device. The eggs are hatched in about twenty 

 days, but the young are not actually born until they are several 

 months old, by which time they are nearly two inches long and 

 are like the parents except in size. 



In all Elasmobranch fishes, fertilisation is internal and the eggs 

 are very large and few in number. The breeding season extends 

 over the greater part of the year, and only one or two eggs are 

 ripened at a time. After it has been fertilised, the egg is enclosed 

 in a brown horny case, often oddly shaped, usually oblong or 

 quadrangular, with a hook or long tendril at each corner. In some 

 rays and the common English spotted dogfish these egg-cases are 

 deposited on the sea-bottom, or their tendrils are twisted round a 

 strand of seaweed. The secure position and the large and un- 

 palatable case protect the developing embryos for several months, 

 after which the young fish, now able to look after themselves, escape 

 through a slit in the egg-case. In most of the dogfishes, as, for 



