1885.] t'KOCEEDlNGS OF UNlTEt) STATES NATIONAL MUSEUM. 143 



structure of the median fins of these embryos is such that, while their 

 marginal lobes somewhat resemble the foetal villi of the mammalian 

 placenta, they differ from the latter in not being received into maternal 

 crypts, which I diligently but vainly sought for on the surface of the 

 folds which depend from the dorsal wall of the ovary. 



The vascular net-work of the ovary by which the maternal blood is 

 brought into indirect contact with the marginal lobes of the vertical 

 fins of the foetuses is derived from a strongly-developed pair of vessels 

 which enter the two anterior coruna of the ovarian sac. These give off 

 branches to the dorsal, thickened wall of the sac and others to the 

 pendent membranes which extend downwards from its roof, between 

 which the advanced foetuses are i^acked in a somewhat irregular 

 manner. 



V. — The development and intrafollicular gestation of Gam- 



BUSIA PATRUELIS. 



During a temporary residence at Cherrystone, Va., in August, 1881, 

 my attention was directed by Col. M. McDonald to the existence of 

 a small Cypriuodont in the fresh-water streams of the vicinity. The 

 females were gravid, the ovaries of most consisting of twenty to twenty- 

 five yellowish eggs about one twelfth of an inch in diameter. This 

 species, which proved to be Gambusia imtruelis of Baird and Girard, 

 does not, as do most other tishes, commit its ova to the care of the ele- 

 ment in which it lives, but carries them about in the ovary, as do most 

 of the members of this family, where they are impregnated and where 

 they develop in a verj^ remarkable manner. 



Of the manner of impregnation of the female we know very little ex- 

 cept from the observations of Mr. Duly, who has related to me what he 

 has noticed in the actions of the adults kept in aquaria in the National 

 Museum. I have appended Mr. Duly's observations at the end of this 

 paper. 



In the adult male, which measures IJ of an inch in length, the anal 

 fin is strangely modified into an intromittent organ for the conveyance 

 of the milt into the ovary of the female ; a tubular organ a])pear8 to be 

 formed by three of the foremost anal rays, which are greatly prolonged 

 and united by a membrane. At the apex these rays are somewhat 

 curved toward each other, and thus form a blunt point, but the fore- 

 most one of the three rays is armed for its whole length with trans- 

 verse ridges, and with sharp recurved hooks at its tip, the other two at 

 their tips similarly with hooks, and between their tips are two small 

 fenestra or openings which possibly communicate directly with the 

 sperm duct from the testes. The basal interspiuous bones of the anal 

 fin are bound together by fibrous tissue into a cylindrical columnar 

 bony mass, truncated above, and is prolonged upwards from the in- 

 ferior abdominal parietes behind the anus into the cavity of the air- 

 bladder lor the distance of nearly the eiglith of an inch ; from the upper 

 truncated end and the posterior side of this column a series of fibrous 



