VIVIPAROUS FISHES OF THE PACIFIC COAST. 
409 
as its parent. The female external genital opening is situated a little posterior to the anal opening, 
the orifice is at its apex, and in the center of a fleshy conical protuberance, which is in fact a powerful 
sphincter muscle, moored, as it were, in its place hy two strong muscular ropes, acting from and 
attached to the walls of the abdomen. 
The above account by Lord, as far as it deals with the embryology, is largely 
conjecture and of no value. It is here given simply to complete the history of the 
work done on these fishes. 
James Blake, Proc. Cal. Acad. Nat. Sci., hi, 314-317, gives somewhat more 
reliable information. His paper is given in full: 
I am not aware that the process by which the embryo of the Embiotocoid fishes receive the 
nourishment necessary for its growth, has ever been pointed out. It certainly differs from the three 
most common forms in which the embryo of other animals is nourished, as there is nothing like a pla- 
centa hy which they can receive nourishment from the mother; there is no supply of nutriment sur- 
rounding the embryo as in the case of most oviparous animals, nor is the embryo brought into direct 
contact with the water, so as to derive nourishment hy absorption from the surrounding medium, as 
is the case in oviparous fishes generally and in most of the lower forms of animal life. The young fish 
is contained in a uterus which, in the undeveloped state, resembles very much the ovaries of the com- 
mon oviparous fishes, except that its walls are thicker, and that the number of ova it contains is very 
much smaller. In the interior of the uterus, projecting from its sides, are a number of processes anal- 
ogous to those to which the ova are usually attached. These processes vary in number in different 
examples, but they are so arranged that each foetal fish is in contact on every side with a surface of 
one of these processes. They consist apparently of a membrane composed of a cellular tissue, and 
scattered over their surface are a number of small mammillary elevations with an orifice in the center, 
and which are probably the organs by which the peculiar secretion of the uterus, to be hereafter 
noted, is poured out. 
In an example I examined, in which impregnation had apparently just taken place, numerous ova 
were found adhering to these processes, although not at all in such numbers as in the ordinary fishes. 
I counted thirty-eight in about the space of an inch ; of these, however, but few can be developed, as 
the number of foetuses seldom exceeds forty, and is sometimes only eight. In the whole of the uterus 
there probably were from one hundred to one hundred and fifty ova. Of the earlier stages of devel- 
opment, however, it is not my object to treat in the present memoir, as I did not commence my inves- 
tigation sufficiently early to be able to fully make it out; as soon, however, as the embryo has 
advanced sufficiently for the fins to be formed, these appendages are found to he terminated hy a 
number of digitations, which project from the free edges of the fin, and are usually found situated one 
between each ray or spine. They are composed almost entirely of fine capillary blood-vessels, united 
apparently by a very delicate and structureless membrane. They are so delicate that unless great 
care is taken in removing the specimen from the uterus, they are destroyed ; nor have I ever been able 
to discover them in specimens that have been preserved in alcohol. These processes seem continuous 
with the membrane extended between the rays of the fins, but are much more delicate; they project 
from the free edge of the fin, sometimes as much as the eighth of an inch, and are, in the fully devel- 
oped embryo, the fifteenth of au inch broad. On the free margin of each digitation, a larger capillary 
can be observed, which appears to be continuous all around; it is about the .003 inch in diameter, the 
intermediate space being filled with a network of smaller capillaries. This system of digitations 
projects from the entire edge of the dorsal, ventral, and caudal fins, but not from the pectorals. They 
in fact form a fringe around the entire body with the exception of the head and that part of the 
abdomen in front of the anus. 
Such is the structure of the organ that evidently has some connection with the fetus, resembling 
as it does so closely the early formation of the vascular villi and the placenta] tufts that proceed from 
the chorion of the mammiferous embryo, and through which it derives its nourishment before the 
placenta is fully formed. 
The question now presents itself as to how nourishment is conveyed from the parent to the 
foetus through these tufts? As before stated, the lining membrane of the uterus sends off processes 
which surround each foetus, without however forming shut sacks; but although these processes are 
very freely supplied with blood-vessels, yet the finest injection failed to show any more vascular spots 
where the fetal digitations might have been brought into more immediate contact with the blood of 
