GREAT BRITAIN. 33 



pleted before it emerges from its parent. In a few forms 

 the young are produced alive. In the hags and lampreys 

 the arrangement is still more simple, the ova when set free 

 descending into the abdominal cavity, and finding its exit 

 at the abdominal pore situated behind the vent. 



In the teleostean or bony fishes we find considerable 

 differences in the form of the male organs, but all have one 

 phenomenon in common, which is a great seasonal aug- 

 mentation in size in such as are not sterile. This, when 

 arrived at maturity, is commonly known as " soft roe " or 

 " milt." Some fishes, although they have not attained any- 

 thing like adult size, are capable of the reproductive process, 

 the milt being fully developed in the male parr, while the 

 female of the same age is usually incapable of propagating 

 its kind, as less nourishment appears to suffice for the pro- 

 duction of milt than is necessary to form ova. Without 

 entering upon the different forms in which these organs 

 exist, it will suffice to remark that when " vasa deferentia " 

 are absent in the males, oviducts are similarly wanting in 

 the females. When the testis is single so is the ovary. 

 In most osseous fishes the ovaries form two elongated sacs, 

 closed anteriorly, but posteriorly continued into a short 

 and wide oviduct, that terminates behind the vent, and 

 mostly before the urethra. The inside of these sacs is more 

 or less lined with the " stroma," or a peculiar tissue within 

 which the ova are developed. In forms in which the ova 

 are hatched before extrusion, the stroma does not extend 

 to the hind portion of these sacs, for this locality serves as 

 a sort of uterus, and is provided, while internal incubation 

 is going on, with an albuminous secretion. 



The various modifications of the generative organs in 

 these fishes are a testis or ovary, without an excretory 



VOL. I. E. I. D 



