Vol. III. 



JULY, 1893. 



Copyright 1893. All Rights Reserved. 



No. 28. 



DENOMINATIVE CHARACTER- 

 ISTICS OF FRESH-WATER 

 FISHES. 



II. 



We come now to the process of re- 

 production in fishes, the organs for 

 which in nearly all are distributed be- 

 tween two individuals, the male and the 

 female. 



The form of the female organs or 

 ovaries, most common among fish, con- 

 sists of two sacs uniting towards the pos- 

 terior end in a single oviduct, which dis- 

 charges outside behind the anus. On 

 their inner surface of these sacs, in 

 nearly all fish, are found leaflets, placed 

 either crosswise or lengthwise, and 

 which contain the eggs in thousands. 

 These increase in number and size 

 when the spawning season arrives, 

 greatly distending the ovarian sacs. 



In some species of fish the ovaries do 

 not present the sac-like form, but re- 

 semble two ribbons (for there are a pair 

 of them) more or less twisted, running 

 along both sides of the intestine to the 

 dorsal wall of the abdominal cavity ; 

 such an arrangement can be seen in the 

 sturgeon and the eel. 



The ripe egg, when it separates from 

 the ovary, passes through a tube (the 

 oviduct), the opening of which as before 

 stated is outside, behind the anus. 



In the male fish the spermatic organs 

 secrete a thick, white fluid, which con- 

 tains innumerable, small, organic 

 bodies which, when in a fresh condi- 

 tion, move about under the eggs, im- 

 pregnate it and start the development 

 of the embryo. These bodies, which 

 are called spermatazoa, consist of an 

 anterior thicker part, the so-called 

 head, and a more attenuated part or tail. 

 In the water these little organisms can 

 live but one or two minutes, but when 

 taken from the fish and put in a bottle 

 kept at the proper temperature, they 

 may be preserved alive for six days. 



This discovery was made by a Russian 

 fish culturist in 1856, and is very im- 

 portant to the artificial propagation of 

 fish, as it enables the crossing of differ- 

 ent species. 



The fecundation of the egg is effect- 

 ed in the viviparous species, inside of 

 the body of the fish, while in the great 

 majority it takes place outside of the 

 body and in the water, wheie the male 

 fish during the spawning season pursues 



