62 J. M. ESSENBERG. 



ture ova of all sizes can be found all over the ovary, but most 

 commonly in the region of the epithelium of the ovarian cavity. 

 Yolk is deposited at the time the ova have reached medium size. 

 At this time the young egg has a beautiful alveolar structure in 

 section due to the presence of oil globules which have been dis- 

 solved by reagents. 



The epithelium of the ovarian cavity of the adult Xiphophorus 

 hclleri differs in no essentials from that of Glaridichthys described 

 by Philippi (1908). Owing to the encroachment of the adult ova 

 it has been thrown into numerous folds which occasionally are not 

 unlike the villi of the small intestine. The characteristic depres- 

 sions in the epithelium of the ovarian cavity called " Delle " by 

 Stuhlmann (1887) are ver y prominent in Xiphophorus helleri. 

 Each depression is an imagination of the epithelium of the ovarian 

 cavity into the ovarian substance directed toward an egg. It serves 

 two purposes : admission of tlfe sperm into the ovum and creation 

 of a place of rupture for the escaping young. Its formation begins 

 with rather young ova, slightly below medium size, but is not com- 

 pleted until the time of fertilization. 



The oviduct of the adult female is very short. It consists of 

 three layers : an outer muscular, a middle connective tissue, and an 

 inner epithelial. The latter is thrown into folds which may either 

 project into the lumen like villi or overlap and form pockets. 

 According to Philippi (1908) these pockets serve as hiding places 

 for spermatozoa in which they may remain and maintain vitality 

 for over 160 days. The oviduct enters the uro-genital sinus at its 

 anterior border, projects backward to open immediately in front 

 of the aperture which is located slightly back of the anus. 



VII. LATE SEX-DIFFERENTIATION OF THE MALE. 



Here are comprised the stages in which spermatogenesis takes 

 place. The size limits vary from 30 to 84.4 mm. in total length. 

 The form index of the sexually mature male averages about 4.2, 

 while the fin ratio is 4.25. 



The various stages of spermatogenesis are rather difficult to 

 describe owing to the fact that cell division has thus far evaded 

 the writer's observation. Of course, the difficulty lies mostly in 

 the proper application of terminology and not so much in the 

 changes that take place. 



