226 "PERFECT-MOUTHED" FISHES 



circular in form. The scales may have a smooth, unbroken edge, 

 when, as has been mentioned they are termed " cycloid " scales, 

 or may be fringed with comb-like teeth and are called "ctenoid" 

 scales. The blennies, however, have no scales at all, and in the 

 eels they are represented by minute vestiges embedded in the 

 skin. The mouth is usually at the end of a snout; the bony jaws 

 are furnished with teeth, and the gill chamber is protected by a 

 broad fold of skin, supported by a complete set of bones, called 

 the gill-cover. 



The eggs of Bony fishes differ from those produced by the 

 Gristly fishes. The eggs of a skate or dog-fish are large, few in 

 number, and consist of the yolk surrounded by the white and 

 enclosed within a tough, fibrous case or shell ; but the egg of a 

 herring or cod consists only of the yolk (containing the germ), 

 which is enclosed in a thin membrane that has no analogy to 

 the shell of a bird's egg or the tough envelope of a skate's egg. 

 The eggs are usually very minute and produced in enormous 

 quantities. (See p. 209.) 



The eggs of Bony fishes are of three kinds light and separate 

 from each other, in which case they are carried about here and 

 there by the currents of the water ; heavy and separate ; or heavy 

 and adhesive. In the last two cases they sink to the bottom of 

 the water. 



The majority of fishes, after shedding their eggs, take no 

 further interest in them, but leave them to the mercy of the sea 

 and the numerous creatures who feed upon them, the consequence 

 being that only a very small percentage arrive at maturity ; hence 

 the reason of the extraordinary fecundity of many fishes. Some 

 species, however, show a certain amount of care and intelligence 

 in providing for the safety of their offspring ; while some are really 

 most devoted parents, and take a great deal of trouble in rearing 

 their young. 



As in the case of the bow-fin which has already been mentioned, it 

 is, curiously enough, almost always the male fish that under- 

 takes the duties of guardian and nurse ; the female, after 

 depositing the eggs, swims away and leaves her mate in sole 

 possession of them ; but in a few cases both parents remain 

 on guard and share the labours of tending the eggs and driving 

 away prowling creatures who would devour them. The Butter- 





