418 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
These observations were taken at San Francisco. At San Diego, 500 miles 
farther south, I have taken the very smallest, less than 100 mm., with ripe eggs, 
March 3, 1889, and segmenting eggs could be obtained throughout January. 
No definite time can, of course, be set for the maturation of the different sizes, 
because there is considerable variation even within small limits of size. This may 
again be due to the age of the fish. The age of the fish would be partly indicated by 
its size, but two fish of the same size may not necessarily be of the same age, since 
the rate of growth is in all probability not uniform in different individuals. 
What I have endeavored to show for Cymatogaster is much more evident for 
Ampliistichus , where there does not seem to be so much gradation in size, but several 
distinct sizes can be separated. These different sizes have also distinct maturation 
periods. It is also quite evident from these lists, and scarcely needs mention, that 
the number of young is directly proportional to the size. I obtained very minute 
mothers at San Diego with but three young, while, as is evident from the above, the 
average number for the largest mothers is 16, the maximum number observed by me 
being 22. 
The ovary . — The ovary is a spindle-shaped bag, divided anteriorly into two arms 
which indicate the bilateral origin of the present structure. One of these arms, the 
left, is usually much smaller than the other, and the blood vessel entering the ovary 
by this smaller horn is also much smaller than that of the other horn. The testes of 
the right and left side are distinct. The ovaries of the two sides have evidently 
been united from behind forward, so that externally only the two anterior horns show 
the bilateral structure, and one of these horns seems to be in process of phylogenetic 
resorption. From the inner upper margin of this bag are suspended two sacks with 
their open ends near the posterior end of the bag. Each one of these sacks is divided 
by a vertical partition similar to their sides into two compartments. 
The ovary lies, in the normal condition, just above the rectum and is suspended 
from the dorsal wall of the abdomen by a mesoarium which is directly continued below 
the ovary as the mesorectum. 
The ovarian walls are composed, first, of the thin peritoneal membrane; second, 
of a layer of longitudinal muscle fibers; third, of a layer of circular muscle fibers, 
inside of which there is, in places, another layer of longitudinal fibers ; fourth, of a 
very thin layer of cells with flattened, deeply stainable nuclei; fifth, of a layer of 
epithelium. This layer is derived from the peritoneum. The cavity of the ovary 
arises as a groove on the outer lateral portion of the germinal ridge. The raised 
margins of the groove unite and form the ovarian cavity, which remains for some time 
connected with the body cavity by a ciliated opening. The inner linings of the ovary 
are thus of peritoneal origin. Laterally and ventrally the two inner layers form 
simple thin linings; dorsally they are thrown up into a number of low ridges. Besides 
these ridges there are on either side of the median dorsal line three broad sheets 
which are simply ridges enormously exaggerated. These sheets are united to form 
the sacks mentioned above. Cross-sections of these sheets show them to be composed 
externally of a continuation of the epithelium lining the ovarian sheath and internally 
by a continuation of the membranous tissue lying immediately outside the lining 
epithelium of the ovarian walls. In other words, Nos. 4 and 5 of the structures 
enumerated above are raised and greatly prolonged to form these sheets. Ventrally 
