610 



COMPAEATIVE ANATOMY. 



in the Cyclostomata. The ovaries of the Petromyzontes have the 

 form of paired lamellas, which extend along the ccelom, and are 

 thrown into a large number of folds, in which the ova are developed. 

 The testes are similar in character. In the Myxinoidea the germ- 

 glands are unpaired, and arise from the right side of the mesentery. 

 Both sets of generative products are passed into the cosloin, whence 

 they reach the exterior through the abdominal pore. 



The ovaries of some Teleostei have almost the same characters ; 

 thus, in the Salmonidas the eggs are passed into the abdominal 

 cavity, and are evacuated through the abdominal pore. The 

 same is the case in Lcemargus borealis among the Selachii, 

 where the ovaries contain much smaller eggs, and are themselves 

 much larger. In the rest of the Fishes there are efferent ducts 

 in both sexes, which are largely — perhaps always — due to the 

 differentiations which affect the primitive kidneys (cf. § 448). 



In this relation the Ganoi'dei are of a low grade, for their 

 germ-glands have no direct ducts, and their products are passed 

 into the ccelom. In both sexes the products escape by an apparatus 

 which is homologous with the Mullerian duct, consisting of a canal of 

 varying length, and provided with an infundibular orifice, which is 

 attached to the ureter (secondary archinephric duct) ; this takes up 

 the generative products. This fact must be regarded as one of 

 special importance, for we learn from it that the Mullerian duct 

 may be turned to use in the male. The presence of this duct in 

 both sexes leads to a correct apprehension of the real facts of the 

 case, and renders it unnecessary to regard the presence of the 

 rudiments of these organs in the male as due to a primitive 

 hermaphroditism, which, cannot be shown to have obtained at the 

 required stage of development. 



Two different arrangements can be derived from that which is 

 dominant in the Ganoidei. One is seen in the majority of the 



ajv 



Fig. 347. Generative organs and enteric canal of Clupea harengus. oc (Esophagus. 



Stomach. ap Appendices pyloricce. i Enteron. a Anus, vn Air bladder. 



pn Air duct, s Spleen, tt Testes, vd Their efferent duct, g Genital pore. 



br Branchiae (after Brandt) . 



Teleostei, and the other in the Selachii, and from thence in the 

 Amphibia and all Amniota. 



The male organs in all Teleostei and the female organs in all 



