OVARY AND OVA IN LUCIFUGA AND STYGICOLA. 231 



the preservation of the species that a multitude of young be produced, as in the 

 case of the oviparous fishes. The condition of viviparity, providing as it does 

 for the greater safety of the young during the most critical period of their 

 development, and their habitat in caves where the number of enemies is prob- 

 ably greatly less than in the sea enable these species to maintain themselves by 

 the production of fewer offspring. 



SUMMARY 



1. The ovary in Lucifuga and Stygicola consists of a mass of stroma containing 

 the ova and covered with epithelium ; the whole structure is V-shaped and is con- 

 tained within the ovisac; the latter is continued to the urogenital pore as the oviduct. 



2. The epithelium, lining the ovisac and covering the ovary proper, is unique 

 in that it frequently contains numerous blood capillaries. 



3. The sinuses within the stroma are filled with lymph and adipose tissue. 



4. Lucifuga and Stygicola are viviparous blind fishes which give birth to but 

 few young, 2 to 15 so far as yet observed. 



5. The young are not developed in separate sacs, but lie within the lumen of 

 the ovisac, gradually compressing the ovarian stroma as they develop. 



6. The ova arise in "nests "or masses of several hundred each. The smallest 

 observed have a diameter of 5 to 10 /A. 



7. One ovum from each "nest" is developed to maturity; the other ova of the 

 "nest" undergo rapid degeneration and are ultimately absorbed into the substance 

 of the large ovum. 



8. In those "nests" in which none attains maturity, all the ova undergo a slow, 

 pigmented degeneration in situ. 



9. The destruction of so many ova at an early stage is an adaptation to the vivipa- 

 rous habit. 



10. Viviparity is probably a comparatively recent acquirement of these fishes, 

 though attained before these genera left the sea for the fresh-water cave streams. 



