132 THE PHYSIOLOGY OF THE COMMON CRAYFISH. 
nucleated cells, separated from the cavity of the organ by 
a delicate structureless membrane. The growth of these 
cells gives rise to papillary elevations which project into 
the cavity of the ovary, and eventually become globular 
Fig. 83.—Astacus fluviatilis.—A, a lobule of the testis, showing a, acini, 
springing from }, the ultimate termination of a duct (x 50). B, 
spermatic cells ; a, with an ordinary globular nucleus n; 6, with a 
spindle-shaped nucleus ; c, with two similar nuclei; and d, with 
a nucleus undergoing division (x 600), 
bodies attached by short stalks, and invested by the struc- 
tureless membrane as a membrana propria (fig. 32, m). 
These are the ovisacs. In the mass of cells which be- 
comes the ovisac, one rapidly increases in size and 
occupies the centre of the ovisac, while the others 
