156 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
THE DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 
GENERAL DEVELOPMENT. 
In well-advanced embryos taken in January (for stage of development, compare 
cut 38) a very minute cluster of cells can be detected on either side of the middle line 
close upon the mesodennic partition which screens the heart from the intestine. 
These cells are mesoblastic in origin; they possess oval or spherical nuclei which, 
however, are not conspicuous for their size. At the time the embryo is about to hatch 
there is less doubt in the identification of the reproductive organ (fig. 116, plate 36). 
It now consists of a small oval, somewhat flattened mass of cells, lying close upon 
the mesentery, next to the intestine. It appears to arise as a proliferation of the 
mesoblast of the mesentery, but at this time is very distinct from it. 
Later, in the first and second larval stages, the reproductive organ is a more com- 
pact, almost spherical, cell mass (about 4 - 4 mm. m diameter). Its position, close to the 
anterior end of the heart, but in contact with the mesentery, is well shown in fig. 174, ov, 
plate 43. It is now differentiated into two kinds of cells: (1) Central cells with large 
nuclei ; (2) peripheral cells with much smaller nuclei (fig. 117, plate 36). The latter 
probably give rise to the ovarian wall, the former to the ova and follicular epithelium. 
The clearer central cells contain a distinct reticulum in which masses of chromatin 
are held. The organ is delicately suspended to the side of the mesentery by connective 
tissue. I did not distinguish the outlines of cells in any part of it. 
In as late as the sixth or seventh stages the reproductive organ is still of very 
small size and not readily seen. 
THE OVARY. 
In a female 44 mm. long (No. 2, table 32) the ovary was of the size shown in fig. 
131. I did not observe the ducts, probably because of the poor condition of the 
specimen when dissected. These were undoubtedly present, since their openings are 
visible in the eighth stage (fig. 89, plate 32 — No. 3, table 34), when the animal is less 
than an inch long. This ovary was 15 mm. long, and each lobe was about one-fourth 
mm. m diameter. The anterior lobes embrace the masticatory stomach, and one of 
the posterior lobes was branched. 
If the condition of the tissue could be trusted — it was preserved in alcohol, 
considerably diluted — the organ now consisted of a distinct connective tissue Avail and 
an inclosed mass of large cells, which are the ova (fig. 146, plate 40). There was no 
plaited or folded ovarian epithelium such as we see at a later stage. 
In a young female 2|| inches long the ovary had the size and appearance shoAvn in 
fig. 132. It is about 40 mm. long and has a diameter of 0.5 mm. It is opaque white. 
In a lobster 4^ inches in length (No. 42, table 20) the ovary has the same appear- 
ance but is somewhat larger. Its structure is now much more complex than at any of 
the stages described. It consists of a thin connective tissue envelope and a compact 
stroma. Folds of epithelium dip down from the surface and penetrate the interior of 
the organ, thus dividing up the outer portions into radial compartments, in which the 
larger eggs are seen. These contain large nuclei, with one, two, or more nucleoli. 
The axis of the ovary lies in a stroma in which all stages in the development of 
ova can be traced. Karyokiuetic figures of dividing cells are not infrequently seen. 
Blood now penetrates to the ovary by sinuses Avhicli come in from the wall along 
reentrant folds of epithelium. 
