FISHES. 351 



Previous to the deposition or ejection of the roe or eggs 

 by the female, a social union has been formed with a male. 

 But this connection is merely temporary, and is dissolved 

 immediately after the impregnation of the egg has taken 

 place. 



The ova are first deposited by the female, and then the 

 male pours upon them the impregnating fluid. In many 

 instances, they mutually form a hole in the sand, and place 

 therein the roe ; in other instances, the roe is deposited in 

 the crevices of rocks, or on sea weeds or aquatic plants. 

 But it would be endless to detail the various ways (even 

 were we better acquainted with them than we profess to be) 

 in which fishes perform this curious function of their na- 

 ture. 



The eggs of fishes are very various with respect to col- 

 our, but agree in being of a spherical form. The integu- 

 ment is more or less firm, according to the species. The 

 yolk, which contains but little oil, instead of occupying the 

 centre, as in the eggs of birds, is placed laterally, and is 

 surrounded by the glaire or albuminous matter. Between 

 the yolk and the glaire is situated the germ or embyro. 

 The germ becomes ready for exclusion at very different pe- 

 riods, according to the species. Thus, the egg of the carp 

 is said to be perfected in the course of three weeks, while 

 that of the salmon requires as many months. But in the 

 eggs of the same species, a great deal depends on the tem- 

 perature to which they are exposed ; as, in the same pond, 

 those eggs are soonest hatched which have been deposited 

 in the shallowest water. 



As the embryo is developed, the heart first appears, af- 

 terwards the spine, eyes, and tail. The organs of motion 

 are evolved in the following order. The pectoral fins first 

 make their appearance, and afterwards those of the tail ; 

 the dorsal fins follow, and then the ventral and anal fins. 



