374 MONTGOMERY — MORPHOLOGICAL SUPERIORITY. [Oct. 7, 



consideration with regard to the relative morphological status of 

 the sexes, nor yet with reference to their bearing upon the ques- 

 tions of phyletic relationship. Relative simplicty and similarity of 

 the genital organs, as in the Invertebrates, is found only in aquatic 

 forms, and in those where there is neither intimate union of the 

 sexes nor intra-uterine development. This condition is realized in 

 most Fishes, Dipnoi and Batrachia. 



Among the Fishes, more especially the Teleostomi (^Ganoidei 2CC\A 

 Teleostei), the testes and ovaries are much alike in structure, usually 

 sacs with more or less folded walls ; this is also the condition in the 

 Acrafiia {Amphioxus). In the Batrachia, particularly the Urode- 

 lia, the testes are more complicated than the ovaries since they are 

 divided into lobes. In the Sanropsida and Mamvialia the ovaries 

 are no longer sacs, but solid cellular masses with follicle cells and 

 germ cells intermingled ; there is always, however, more or less of 

 a radiate lobulation of the organ. The testes of the same forms are 

 composed each of masses of tubules, of which the walls are made of 

 cells of Sertoli and early generations of spermatogonia, while their 

 lumen becomes filled with more mature germ cells. There can be 

 no question that in the higher Vertebrates the testes are more com- 

 plicated than the ovaries, the reverse of the case in the Inverte- 

 brates. But while the testis is morphologically more complex, it 

 nevertheless retains primitive embryonic structures more than does 

 the ovary. For the vasa afferentia, namely, of the testis, as at least 

 the proximal portions of the vasa efferentia (these together consti- 

 tuting the tubules of the testis), represent persistent mesonephric 

 tubules, the second kidney system of the embryo ; these persist in 

 only very rudimentary form in the ovary. From this standpoint 

 the testis, while more complex, is concurrently less progressive ; the 

 ovary, though structurally simpler, has changed more in the course 

 of the ontogeny.^ 



The gonads are primarily paired in the Vertebrates, except in 

 the Cyclostomata. When in higher forms there is degeneration of 

 one of the pair it is always an ovary, as in Birds, and never a 



1 In regard to the comparison of the testis and ovaiy, it becomes obvious that 

 greater complexity of structure, or specialization, does not imply greater morpho- 

 logical advancement of its possessor, unless it is associated vv^ith correspondingly 

 greater change in the ontogeny. So an extreme parasite, as Tcznia, is structur- 

 ally simpler than its free-hving ancestor, though in point of phyletic change it is 

 far more advanced. Regressive development is still development. This is an 

 important consideration which anatomists do not always appreciate. 



