556 PROF. G. B. HOWES ON SOME 



the views hereiu put forward {cf. p. 552). Indeed, the study of 

 Lepidosteus, and of the facts just briefly alluded to, suggests — if 

 it be granted that the Chordata were primitively hermaphrodite, — 

 that the diff"erentiation of the Wolffian and Miillerian ducts 

 was associated with the first step towards unisexuality, and that 

 the presence of remains of the one or other of these ducts in the 

 opposite sexes of the Vertebrata in the form of a non -functional 

 A-^estige is far from being an index of hermaphroditism, as has 

 been frequently supposed. 



My friend Prof. W. JN". Parker has lately shown * that in Pro- 

 toptenis Miillerian ducts are present in both sexes. He has 

 further made the very important discovery f that in the male 

 vasa efFerentia are absent, the testis-duct being, like that of 

 Osteichthyes, continuous with its gland — or, to state the facts 

 otherwise, that epididymis and vas deferens are unrepresented. 

 Erom my standpoint two most striking conclusions arise from 

 this, viz. : — (a) tliat in the perfection of uuisexuality the formation 

 of the Miillerian duct must have preceded that of the vas deferens ; 

 and (/3) that the Dipnoi must have struck off from the parent 

 stock during the interval in the differentiation of the two J. 



The living Vertebrata, as classified by their urino-genital system, 

 fall into two readily discernible series, viz. : — (a) the Ne'pliror- 

 chidic series, embracing the Elasmobranchii, Amphibia, and 

 Amniota, in which vasa etferentia are present and the excretory 

 organ is an accessory to reproduction in the male ; (/3) the EutTior- 

 c7iidic§ series, embracing the Ganoids, Teleostei, Marsipobranchii, 

 and Dipnoi, iu which vasa efterentia are unrepresented, and the 

 "Wolffian or segmental duct is exclusively renal iji function. 

 That the latter type must be looked upon as the more primitive 

 is clear, from all recent discovery in the morphology of the 



* Berichte d. naturf. Gesellsch. Freiburg i. B., Bd. iv. Heft 3, p. 22 (1888). 



t As yet UDpublisbecl. I here acknowledge my indebtedness to him for 

 permission to mention his observation. 



X It follows from this that whatever be the affinities of the Dipnoi, they can 

 have nothing to do with living Ganoids. Indeed they appear to me to have left 

 the Holocephahc branch of the Elasmobranch stock prior to the differentiation 

 of the immediate ancestors of its living members. In this belief and iu my 

 views of the inter-relationships of the Ichthyopsida, I find myself in complete 

 harmony with Beard {cf. Anat. Anz. 1890, p. 186). 



§ eu6v?, straight. 



V' fii - /-^/7 



