1 84 CHILDHOOD OF ANIMALS 



of most fishes secretes an abundant mucus from little glands some- 

 times opening directly on the surface, sometimes into a set of 

 canals on the head and sides of the body. The secretion no doubt 

 helps to keep the skin smooth and soft and more fit to glide through 

 the water, and is also useful in washing off the spores of moulds 

 and fungi and other harmful parasites which might otherwise settle 

 on the body. It may also be protective by being offensive to other 

 animals. Living fish which have been captured and put in a 

 bucket of water usually discharge large quantities of mucus ; two 

 or three hagfish put in a bucket may give off so much that the 

 sea-water almost sets in a jelly. Frogs, toads and newts also give 

 off an abundant slime which, besides its other useful properties, 

 certainly has an offensive taste and protects them from being 

 swallowed by many animals. A dog will not try to eat a frog or 

 toad twice. In reptiles the skin glands are not so profusely 

 scattered over the body ; they are larger and arranged in definite 

 places, and the skin as a whole is dry. Why so many persons 

 believe that serpents are slimy I do not know ; their skin is always 

 absolutely dry. In lizards there are usually rows of skin glands 

 along the inner side of the thighs ; in turtles and tortoises on the 

 soft skin between the junction of the upper and lower " shells," 

 and sometimes under the chin. Crocodiles have large skin glands 

 on the lower jaw, and snakes near the anus, whilst in some there 

 are smaller glands near the edges of the mouth. It is certain in 

 some cases and probable in others that the secretions of these 

 large glands have a strong odour, often musky or disagreeable 

 and often discharged when the animal is annoyed, as in the well- 

 known case of the common English grass snake. In birds the 

 skin generally is not glandular. There is a very large gland, the 

 preen gland on the back, with a nipple from which an oily secretion 

 is discharged, which the bird smears on its beak and uses to 

 preen the feathers. In some of the aquatic birds there is a pair 

 of glands on the lower jaw. 



These various glands are protective, or odoriferous, and may 

 advertise the presence of their owners at the breeding time, but in 

 no case is their secretion employed to feed the young. In mammals 

 there are various masses of skin glands secreting odoriferous 

 substances in different parts of the body : on the feet of ruminants, 

 on the legs of horses, on the fore-arms of lemurs, on the tails of dogs 

 and wolves, on the backs of peccaries and hyraces, on the faces 

 of antelopes and deer, on the temple of elephants, near the anus 



