OVARIAN STRUCTURES OF VIVIPAROUS BLIND FISHES. 4! 



statements are now either matters of common knowledge or else 

 not in accordance with the facts as revealed by later investiga- 

 tions, I shall not speak of their work further. 



Wyman (op. cit.~) classifies viviparous fishes into two groups 

 "according to the position occupied by the embryo during the 

 period of growth. In the first group may be arranged those 

 fishes in which the ovum leaves the ovary in an undeveloped state, 

 and in which the process of eolntion (sic] is not commenced until 

 it readies the lower portion of the oviduct. The fishes which this 

 group comprises are nearly all, if not all, Plagiostomes. The 

 best known are Spinax, Carcharias, Mustcllus, Galeus, and 

 Torpedo. ... II. In the second group those fishes are comprised 

 in which the gestation is wholly or in part ovarian, the last stages 

 only of the process usually occurring in the oviduct. Among 

 the genera included in this division are Sihirns, Blcnnius, Ana- 

 bleps, Ptfcilia and Embiotoca. In all of these genera impregna- 

 tion takes place in the ovary, and, as seems probable, while the 

 ovum is still invested with its original envelopes." 



Wyman found that each of the foetuses in A. gronovii is envel- 

 oped in a separate sac of vascular tissue, much too large for the 

 foetus enclosed, the extra space being filled up with an albuminous 

 fluid. He seems to regard these foetal sacs simply as extensions 

 of those within which the ova were suspended. 



Eigenmann, considering only teleosts, found two types of 

 viviparity (op. cit., p. 404) ; he says : 



" At least two types of viviparity may be distinguished in 

 fishes ; first, those in which the yolk furnishes all the intra- 

 ovarian food ; and second, those in which the greater part of the 

 food is furnished by the ovary. 



" In the first type the number of young is not less than in re- 

 lated oviparous forms, while the number of young in the second 

 is always greatly reduced. . . . The size and development of 

 the young in this class (type I.) of fishes at the time of birth is 

 of course much less than in the second class of viviparous 

 fishes." 



As will be seen, Lucifuga and Stygicola belong to the second 

 type of both Wyman and Eigenmann. The number of young is 

 small and they are born in quite a mature condition. 



