FISHES — EMBIOTOCOIDAE. 165 



are generally thinner, more closely set togeilier, and less divided than the posterior ones. A 

 membranous, sub-tubercular growth upon the base of the anterior soft rays of the latter fin will 

 distinguish males from females. The caudal fin is generally more or less forked. The ventrals are 

 sub-thoracic, and provided exteriorly with a strong spinous ray. In most genera a naked area 

 may be detected along the middle of the belly between the ventral fins and the anal, and partly 

 overrun anteriorly by a lanceolated scaly blade inserted between and near the base of the 

 ventrals. 



But the most remarkable trait in the organization of the fishes of this family consist in the 

 mode of reproduction. The eggs, instead of being laid, as is the case in most fishes, are retained 

 ■within the body of the female, where they undergo, not only their embryonic growth, but like- 

 wise a growth which might be termed larval, it being subsequent to their escaping from the egg 

 envelope, until they have attained a size sometimes of several inches in total length. Never- 

 theless, this peculiarity of habits is not altogether without analogy in the class of fish. Moreover, 

 it bears no resemblance whatever to the marsupialian gestation : in the first place the eggs 

 develope in the ovary, not in a uterus, and there is no placental connexion of any sort; secondly, 

 the young are not at liberty to quit and enter the ovarian cavities alternately and at pleasure. 

 The observations which we have made upon the genital apparatus of the female have satisfied us 

 that there exists an ovarian sheath or sack, which, during the early period of pregnancy, is an 

 elongated and sub-cylindrical tube, containing the ovaries proper, two in number, each of which 

 consisting of two, three, or more vascular membranes, attached by their upper eJge to the upper 

 floor or roof of the sheath, forming either one or two pouches (according to the number of these 

 membranes) of the same length as the sheath itself, widely open beneath, though not in direct 

 communication with one another, since the membranes hang loosely down, reaching the lower 

 floor of the sheath. 



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

 examined the ovaries of Ennichtliys Jieermanni and Emhiotoca argyrosoma 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 unarmed eye like minute dots. Under the 

 microscope (Plate XXVI, fig. 9), they exhibited evident traces of the germinal vesicle surrounded 

 sa yet with a very scanty supply of vitelline substance. 



The sheath and the ovaries are gradually increasing in bulk, as the eggs themselves first 

 increase in size and the embryos afterwards. The sheath is chiefly a muscular membrane, 

 whilst the ovaries, we have stated, are altogether vascular. 



When mature, 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 a corpus luteum or a graflian vesicle. 

 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 individual young, when removed sideways 

 from the ovary, appears to the operator as though enclosed in a separate cavity, pouch, or 



