ANATOMY OF LIMNOCNIDA TANGANYICA. 275 
is the same in both males and females. It is only the ecto- 
derm which is different ‘in the two sexes; but in both, the 
general type of structure of the germarium is similar. 
In both spermarium and ovarium of Medusx the Hertwigs 
distinguish three layers, viz. I, a basement layer; II, a layer 
of germ-cells in various stages of development ; and III, a cover- 
ing epithelium. In Limnocnida, layers I and II are so 
intermingled that it is hard to draw a hard-and-fast line 
between them (figs. 3 and 4). 
The cells which correspond to layer I lie next the mesoglea. 
Their nuclei are relatively large and round. Inthe male there 
are usually several layers of cells, all of the same nature. In 
both sexes these cells may be regarded as the germ mother- 
cells, and it is from them that the cells of the next layer 
originate. 
Layer II is composed of ova or spermatozoa in various 
stages of development. On comparing sections taken through 
the germaria of the two sexes (figs. 3 and 4) the general 
distinguishing features are strikingly brought out. In the 
male the germ-cells tend to become as numerous and as small 
as possible, while in the female all available material is 
employed in the construction of a few gigantic ova. In 
the section of a spermarium shown in fig. 4, two stages 
of development are seen. The innermost cells have large 
round nuclei, nearly twice as large as the nuclei of the parent 
cells from which they are derived. These cells eventually give 
rise to clusters of numerous cells with very small nuclei, which 
stain more deeply than those of the large cells. Ata later 
period these small cells will probably grow tails and become 
mature spermatozoa, but among the specimens examined none 
were found with mature spermatozoa developed. 
In the female the cells of the second layer are much larger 
and fewer in number than in the male. It is composed of two 
kinds of cells (fig. 3, ov. and st.), both of which are derived 
from the first layer. The most conspicuous cells in this middle 
layer are ova (fig. 3, ov.), and attain to a very considerable size. 
They are by far the largest cells in the body of the Medusa, 
