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U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
follicle of the ovary, whilst in reality the membranes may he stretched out or extended, and 
the entire progeny loosened from all adherence or connexion with them. 
The male organs of generation consist of two spermaries, a right and a left, perfectly inde¬ 
pendent from one another, having each its separate duct, discharging their contents into an 
elongated cloaca, into which the bladder likewise empties its contents. This cloaca commu¬ 
nicates with the exterior by a sub-circular opening, the edge of which being rather protruding. 
Such is that apparatus : the same in its general structure as in the other osseous fishes. There 
is no sheath enclosing the two spermaries, and this fact throws a considerable light upon the 
morphology of the ovaries ; the latter being, in fact, two in number, but so closely connected 
together as to simulate a single organ. Thus the general disposition, not the - plan of structure, 
of these organs, is adapted to the mode of reproduction ; a single sheath being a more simple 
adaptation than two, one for each ovary. 
How the mechanical act of fecundation takes place we are not prepared to say from direct 
observations : the eggs themselves must be fecundated within the ovarian sheath ; a copulation 
of some sort is, therefore, required, and it is not improbable that at this period the eggs have 
dropped from the ovarian membranes into the pouches or spaces between these membranes, in 
which they are freely floating. 
There are a few points in the history of the development of the young which may be 
deduced from partial observations represented on Plate XXVI. 
The hatching of the embryos takes place at an early period. After leaving the egg shell 
they have an abdominal bag containing the remaining yelk which is to be gradually absorbed 
during a period when neither the mouth nor the esophagus are formed. The fins are as yet 
undeveloped (figs. 1 and 2). The eyes begin with a deposition of an external layer of black 
pimentum, in every respect similar to the same organs in invertebrata (figs. 1, 3, and 5). The 
head is anteriorly rounded, and the cleft of the mouth not yet apparent at the period when the 
fins begin to develop (fig. 1). The caudal has the start over all the other fins ; its posterior 
margin is first lanceolated, then rounded, with a convexity gradually diminishing until it is 
perfectly straight, when a gradual emargination commences, and from a slight crescent reaches 
the forked shape which it has in the adult. The soft and articulated portion of the dorsal and 
anal fins next assume a development reaching extraordinary proportions, which they again 
gradually loose so soon as free from parental sheltering. The posterior portion of these fins is 
especially to be noticed as longer or deeper than the anterior portion (the reverse of what we 
observe in the adult), and extending generally beyond the base of the caudal fin, a character, 
therefore, not exclusively proper to the genus Rhacoclieilua. The spinous portion of these same 
fins, on the other hand, develop but slowly and gradually, reaching their full growth at a late 
period. The ventrals and pectorals are likewise tardy in their appearance. The scales are 
fully developed before the young leave the ovarian sheath. 
The first notice that was made public in relation to these fishes appeared in November, 1853, 1 
with additional remarks in May, 1854. 2 New species of that family were likewise subsequently 
described. 3 But the real knowledge of the remarkable peculiarities concerning some of their 
habits was obtained in the spring of 1852 by Dr. Thomas H. Webb, while attached to the 
* Amer. Journ. of Sc. & Arts, second series, vol. xvi, p. 380. 
2 Ibid., vol. xvii, p. 365. 
3 Proe. Acad, Nat. Sc. Philad. VII, 1854, pp. 105, 122, 134, and 151. 
