the Development of Anableps Gonovii. 435 



II. In the second group those fishes are comprised in which 

 the gestation is either 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, Silurus* Blen- 

 niusrf Anableps,% Pcecilia,§ and Embiotoca.\\ In all of these 

 genera impregnation takes place in the ovary, and, as seems 

 probable, while the ovum is still invested with its original en- 

 velopes. In Blenny, Rathke has shown, the ovarian gestation 

 having continued about three weeks, that about the end of Sep- 

 tember the sac ruptures, and that the embryo is discharged into 

 the central cavity of the ovary, which is in fact the oviduct ; 

 here the foetus remains till the beginning of January, when it 

 is born. In Poecilia the fetus is liberated and escapes into the 

 oviduct towards the end of gestation. Valenciennes has given 

 several details in relation to the development of Anableps Gro- 

 novii, made for the most part upon specimens in an advanced 

 stage of fetation, the smallest embryo being more than an 

 inch long. He found only seven or eight fetuses in the so- 

 called uterus of each female, and each of the young was sur- 

 rounded by a distinct sac, which he regards as simply an 

 enlargement of the original envelope of the ovum. The 

 mature foetus he found to be more than one fourth as long 

 as the parent, and except for the non-development of the 

 ovary, was constituted in every respect like the adult, as re- 

 gards both its internal and external structure. 



For the specimens of Anableps Gronovii, upon which the 

 following observations were made, I am indebted to the 

 liberality of Dr. Francis W. Cragin, United States Consul at 

 Paramaribo, in Surinam. Among them were three males and 

 five females, four of which last were in different stages of ges- 

 tation. The different individuals varied from three and a 



* Cuvier et Valenciennes Hist. Nat. des Poissons, T. i.p. 540. 1828. 

 t Kathk£, Mem. sur la Develop, de 1'Homme et des Animaux, 2me partie. 

 Leipsic, 1833. 



X Cuv. and Valenciennes, Hist. Nat. des. Poiss. T. xviii. p. 245. Paris, 1846. 



§ Duvernoy, Ann. des Sc. Nat. T. I. N. S. p. 313. 1844. 



|| Agassiz, Am. Journal of Science. Vol. XVI. Second Series^ Nor. 1853. 



