140 THE URINOGENITAL ORGANS OF VERTEBRATES. 



method of splitting for the female for the male the splitting is 

 according to Professor Semper, of a more partial character, and 

 consists for the most part in the front end of the duct only 

 being separated off from the rest. The result of these changes 

 is the formation in both sexes of a fresh duct which carries 

 off the excretions of the segmental involutions, and which I 

 shall call the Wolffian duct while in the female there is formed 

 another complete and independent duct, which I shall call the 

 Miillerian duct, or oviduct, and in the male portions only of 

 such a duct. 



The next change which takes place is the formation of an- 

 other duct from the hinder portion of the Wolffian duct, which 

 receives the secretion of the posterior segmental tubes. This 

 secondary duct unites with the primary or Wolffian duct near 

 its termination, and the primary ducts of the two sides unite 

 together to open to the exterior by a common papilla. 



Slight modifications of the posterior terminations of these 

 ducts are found in different genera of Selachians (vide Semper, 

 Centralblatt filr Med. Wiss. 1874, No. 59), but they are of no 

 fundamental importance. 



These constitute the main changes undergone by the seg- 

 mental duct of the kidneys and the ducts derived from it ; but 

 the segmental tubes also undergo important changes. In the 

 majority of Selachians their openings into the body-cavity, or, 

 at any rate, the openings of a large number of them, persist 

 through life ; but the investigations of Dr Meyer 1 render it 

 very probable that the small portion of each segmental tube 

 adjoining the opening becomes separated from the rest and 

 becomes converted into a sort of lymph organ, so that the open- 

 ings of the segmental tubes in the adult merely lead into lymph 

 organs and not into the gland of the kidneys. 



These constitute the whole changes undergone in the female, 

 but in the male the open ends of a varying number (according 

 to the species) of the segmental tubes become connected with 

 the testis and, uniting with the testicular follicles, serve to carry 

 away the seminal fluid 2 . The spermatozoa have therefore to 



1 Sitzen. der Naturfor. Gesdlschaft, Leipzig, 30 April, 1875. 



2 We owe to Professor Semper the discovery of the arrangement of the seminal 

 ducts. Centralblatt f. Med. Wiss. 1875, No. 12. 



