1855.] 319 



floor or roof of the sheath, forming either one, two, or more pouches (according 

 to the number of these membranes) of the same length as the sheath itself, widely 

 open beneath, though not in a direct communication with one another, since the 

 membranes hang loosely down, resting on the lower floor of the sheath. 



The eggs are formed within the texture of the ovarian membranes themselves. 

 We have examined the ovaries of Ennichthys heermanni, when the sheath, within 

 which they were contained, was not larger than an ordinary quill. Numerous 

 eggs could be observed in a very immature state, appearing to the naked eye 

 like minute dots. Under the microscope, they exhibited evident traces of the 

 germinal vesicle, surrounded as yet with a very scanty supply of vittiline sub- 

 stance. 



The sheath and the ovaries are gradually increasing in bulk, as the eggs them- 

 selves first increase in size and the embryos afterwards. The sheath is a mus- 

 cular membrane chiefly, whilst the ovarian membranes, we have stated, are 

 altogether vascular. 



When miture, the eggs either fall into the space between the membranes or 

 ovarian pouches, or else remain attached to the ovaries until the embryos issue 

 out of them. We are inclined to think that they drop into the pouches as eggs. 

 At any rate, we found very young embryos loosely contained in the ovarian 

 pouches, when no trace of the egg membrane could be seen within the tissues of 

 the ovaries in the shape of corpora lutei or graffian vesicles. Whatever be the 

 case, numerous eggs or embryos may be observed within one pouch. The young 

 thus remain together until grown to a considerable size, when, filling up the 

 space in a more compact manner, the ovarian membranes, in their nature very 

 expansive, will extend a fold between each embryo. In this manner every indi- 

 vidual young, when removed sideways from the ovary, appears to the operator 

 as if enclosed in a separate cavity, pouch, or follicle, of the ovary, whilst, in 

 reality, the membranes maybe stretched out or extended, and the entire progeny 

 loosened from all adherence or connection with them. 



The male organs of generation consist of two spermaries, a right and a left, 

 perfectly independent from one another, having each its separate duct, dis- 

 charging their contents into an elongated cloaca, into which the bladder, like- 

 wise, empties its contents. This cloaca communicates with the exterior by a 

 subcircular 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 con- 

 siderable 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 mem- 

 branes into the pouches, or spaces between these membranes, in which they are- 

 freely floating. 



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 have not yet appeared. The visual organs begin 

 with a deposition of an external layer of black pimentum, in every respect similar 

 to the same organs in invertebrata. The head is anteriorly rounded, and the 

 cleft of the mouth not yet apparent at the period when the fins begin to develop, 

 The caudal has the start over all other fins ; its posterior margin is first lanceo- 

 lated, 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 assumes in the adult. The soft and articulated 

 portion of the dorsal and anal fins, next assume a development reaching extra- 



