Characteristics of the Vertebrata. xxxv 



Whether the respiration of Vertebrata be aquatic or aerial^ the 

 apparatus by which it is effected is always connected with the 

 commencement^ and never^ as in some Invertebrata^ with the outlet 

 of the digestive tract. The efferent ducts, on the other hand, of the 

 renal organs, are usually confluent and always in near relation with 

 the anal, and also with the generative outlets. In Plagiostomous 

 Fishes, and in all Vertebrata above the Amphibia, a primordial as 

 well as a secondary kidney is developed; and in all cases, ex- 

 cept those of the Cj/closlomi and Amphioxus, the renal are closely 

 connected either in their development, or throughout life, with 

 the generative glands. When a primordial kidney, the so-called 

 ' Wolffian body,^ is replaced by a secondary and persistent kidney, 

 the provisional gland and its efferent ducts are in the male sex 

 partly converted into spermatic ducts, the so-called epididymis and 

 vasa deferentia, and partly remain as the rudimentary ' cyst of 

 Morgagni,^ and ' organ of Giraldes ' of the class Mammalia ; whilst 

 in the female sex the primordial kidney and a certain part of its 

 efferent apparatus become atrophied, and are known in Mammals 

 as the 'organ of Rosenmiiller ^ or 'parovarium,'' and the 'canals 

 of Gaertner ' respectively ; and the remaining part of the efferent 

 apparatus, the so-called ' duct of Miiller,'' becomes the functional 

 oviduct. In the males of Amphibia, where no secondary kidney 

 is developed, the efferent testicular ducts pass through the anterior 

 part of the substance of their functional kidney, which in higher 

 animals becomes limited to the functions of an epididymis ; and 

 these ducts are, on the distal side of the urinary gland, known as 

 'vasa uro-spermatica.' The posterior part of their functional 

 kidney is exclusively urinary in function, and its ducts may 

 coalesce more or less completely before joining the (Miillerian) 

 duct, into which the uro-spermatic vessels from the anterior part 

 of the gland open; foreshadowing thus the more perfect dif- 

 ferentiation of these structures which we meet with in the air- 

 breathing Vertebrata. According to some authorities, however, 

 the duct of Miiller, the parovarium, and the epididymis are deve- 

 loped independently of the Wolffian bodies and their ducts. This 

 appears to be certainly the case in Mammals 



In the A)npJnoxus, the brain can scarcely be said to exist at 

 all, being represented merely by the nervous tissue surrounding 

 the open ventricle, which is formed by a slight expansion of 



c 2 



