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Part III. — Thirteenth Annual Report 



evolved phylogmetically in the chordata, we have an explanation of the 

 facts of earlier maturation of the males. 



There appears also to be some proof for this in vertebrate ontogeny, 

 for Laulanie* holds that the sexual glands in the fowl pass through 

 three chief stages ; first, that of sexual indifference or germiparity ; second, 

 that of hermaphroditism (very short in the fowl) ; and, thirdly, that of 

 unisexuality. The same stages, with modifications, are found in mammals. 

 The facts he gives are meagre, but are to some extent supported by 

 other observers. 



As regards the comparative frequency of hermaphroditism in the 

 Teleostei, Howes f explains this upon the assumption that they 1 have 

 ' retained a more primitive condition of the genital glands than have 

 ' the other Gnathostomata.' 



From this follows the assumption that the intimate connection of the 

 urinary and genital systems, as exemplified in the Elasmobranchii, 

 Amphibia, and Amniota, is secondarily acquired in these groups. Without 

 entering into a discussion on this subject, a consideration of the primitive 

 relationships of the gonads and nephridia of other Ccelomata, such as the 

 Annelida and Mollusca, would cause one to hesitate before accepting such 

 a far-reaching hypothesis.* Although we have it given upon Professor 

 Howe's authority that ' all recent discovery on the morphology of the 

 ' uro-genital system ' makes his hypothesis ' clear,' yet it is directly 

 antagonistic to the facts of the ontogeny of this system as shown by 

 Boveri | in Amphioxus (where the gonadic cavity communicated directly 

 by the pronephric funnel to the exterior), and Riickert, § Van Wyhe, and 

 others. 



In estimating the greater frequency of occurrence of this particular 

 abnormality in the Teleostei, the immense number of specimens of this 

 group which come under observation should be taken into consideration, 

 the same factor probably accounting, to some extent, for the fact that, 

 amongst the Amphibia, the Anura are similarly conspicuous. 



The more frequent occurrence of this phenomenon in Anura would not 

 warrant our trying to prove the arrangement of the uro-genital organs in 

 them to be more primitive than in other Amphibia. The hypertrophy of 

 the gonads in most Teleostei, in correlation to the necessity for the pro- 

 duction of an immense number of young in order to maintain the exist- 

 ence of the species, may perhaps be a factor in the assumption of the 

 idiodinic type in this group. 



The second of the theories above referred to has recently been put 

 forward by Pilseneer.|| He explains the appearance of hermaphroditism 

 in Pisces and in Mollusea, &c, as being due, not to atavism but to an 

 incipient evolution of the hermaphrodite from the dioecious condition. 

 In the Mollusca he traces the gradual specialisation from the indifferen- 

 tiated hermaphrodite condition to that in which special organs and ducts 

 occur ; but quite granting that in this case and in the Teleostean fishes 

 (Serra?ius, &c), the hermaphrodite condition had been envoi ved within 

 the group, we cannot follow him in his generalisation that ' hermaphro- 

 ditism is secondary and. succeeds a primitively dioecious state] and hence 

 that the unisexual condition is the more primitive. 



If we accept the generally received hypothesis that unisexuality is 

 acquired and is the higher type, then we shall expect to find the 

 hermaphrodite condition either perpetuated or re-evolved only in groups, 

 which are in the first case primitive, or in the second case placed in an 



* Comptes Rendus, 1885, p. 393. f loc. cit. 



X Zool. Jahrbiicher, Abth. fiir Mysh. , 1892. 

 § Ergcb. Anat. Enthick, 1891 (Meikel und Bonnet). 

 |, Quart. Journal Mic. Sci., 1894. 



