250 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
quite small and uniform in size, but mucli smaller than the blood corpuscles of the 
animal. No traces of a racemose, glandular structure is visible anywhere in sections 
of the organ, such as would be necessary in order to constitute it a true pancreas. 
The viscera hitherto considered lie either altogether, or for the most part within 
the body-cavity, as the air-bladder, for example, and all are intimately connected with 
or form a part of the alimentary apparatus. The ovary and testis which are to be 
next described lie within the body-cavity, but their functions are carried on in connec- 
tion with passages or outways, the genito-urinary canals, which lie immediately exter- 
nal to the general body-cavity, and just dorsal of it on either side of the median line. 
The great size of the ovary and testis or milt in the adult contrasts most remarka- 
bly with their small size in the young animal, 7 to 9 inches long, in which the internal 
generative organs, ovary and spermary, are represented by a pair of very slender 
whitish cords or low folds which lie on either side of the mesentery and on the dorsal 
wall of the a'bdominal cavity and diverge from each other from behind forward. Pos- 
teriorly, as shown in the Figs. 51 and 52, the genital folds G B, as the rudiments of the 
reproductive organs may be called in the young sturgeon, lie just internal to the course 
of the spacious genito-urinary ducts which converge to a common median outlet situ- 
ated immediately behind the anus. They do not extend for the whole length of the 
abdominal cavity, but only along the middle half of its length. 
In this first stage of the development of the reproductive tract there are protova 
present, as the first traces of the reproductive elements are called, and which in the 
early stages are very similar in both the ovary and the testis. 
The reproductive elements are derived from the germinal epithelium of the genital 
folds; this epithelium, however, covers only a small portion of the surface of the genital 
folds and only becomes distinctly marked off to the naked eye at a considerably later 
stage. At this stage the tract of genital tissue is a more distinct, flattened, yellowish 
cord than in the younger 7-inch stage, and varies in width from one-eighth to one- 
fourth of an inch. On its inferior side in the young female there is present a well- 
marked band of closely opposed transverse ridges which extend across about one third 
or one-half its lower surface. This series of transverse ridges is guarded b\^ a flap 
or fold at either edge, and sections show that the ridges contain the young ova. The 
development of the testis does not show this longitudinal series of short transverse 
folds at any stage. In cross-section at this stage, the reproductive tissue proper is 
found to include only about one-fourth of the whole genital fold, the remaining part 
of the organ being composed of minute undifferentiated connective tissue which con- 
tinues to grow for some time, and represents the homologue of the fatty body appended 
to the internal reproductive organs in anurous batrachians and reptiles. The numer- 
ous transverse ridges which are found on the inferior side of the genital cords are in 
fact parallel laminae which extend down into the substance of the organ for about half 
of its thickness. These laminae are far more numerous at this stage than the lobules 
of the mature ovary, so that it is obvious that some of them must degenerate in the 
course of the further development of the organ. 
The subsequent stages by which the genital ridge is converted into the ovary or 
testis with an accompanying establishment of the sex of the individual has not been 
fully traced, but it is certain that the conditions observed in the stage last described 
are not much subsequent to the time when the protova or primitive germinal cells 
common to young individuals of both sexes, first make their appearance. The method 
