1 86 



DEVELOPMENT OF FISHES 



n 



and somewhat adhesive; they are deposited in ** nests," i.e. 

 bowl-like depressions, and are attended by the male fish.* 

 Other adhesive eggs are those of carp, Christiceps, Batra- 

 cJuis. Eggs of Salmonids are deposited loosely in '* nests " 

 on a clean, gravelly bottom ; their membranes are thick 

 and parchment-like. On the other hand, the majority of 

 pelagic fishes produce eggs which float (Figs. 196, 197) ; 

 of these the membranes are extremely hygroscopic and 

 transparent, and an oil globule, located in the yolk region 

 of the ^gg, serves to diminish its specific gravity. The 

 ^2^^ membranes of a number of Teleosts, e.g. Blennies 

 (Fig. 199), appear essentially shark-like; a horn-like cap- 

 sule is evolved, whose terminal processes afford it a firm 

 attachment. Aberrant modes of oviposition are not lack- 

 ing ; the South American Siluroid, Aspredo, as is well 

 known, carries its eggs attached to its ventral surface ; the 

 pipe-fishes and sea-horses, SipJiostoma^ Soleno stoma, Hip- 

 pocampus, have specialized a pouch-like fold of the abdo- 

 men and of the ventral fins, which serves to retain the 

 eggs and larvae. It is curious to note that this remark- 

 able condition occurs only in the male. 



The breeding habits of Teleosts are in general like those 

 of Ganoids ; their spawning season is usually during the 

 spring and summer, but is seldom of very brief duration. 

 The hatching of the eggs depends largely upon water 

 temperature, and may vary from a few days to several 

 months (Salmo). 



B. THE FERTILIZATION PHENOMENA 



The processes of the maturation and fertilization of 

 the egg have as yet shown but minor differences in the 



* In several genera they are carried about in the gill chamber of the male, 

 thus ensuring aeration. 



