DESCRIPTION OF THE PLATES. 117 



the secondary. As described in the text, the 

 spermatheca appears to be the organ in which 

 the seminal fluid undergoes the final and essential 

 change which fits it for impregnation. 



PLATE IY. Fig. 4. This figure shows the adult seminal secondary cells 

 from the dilated part of the seminal tube. They 

 are full of tertiary cells. The fluid amongst which 

 they are floating is thick and albuminous, much 

 more so than it is higher up or lower down the 

 tube, and the large, clear, transparent looking 

 masses, are the pabulum for the nourishment of 

 the cells. It is much more abundant in this 

 part of the organ than any where else, and ac- 

 cordingly great numbers of the secondary cells 

 in all stages of developement, are constantly 

 found here. If a small quantity of the seminal 

 fluid from that portion of the testicle immedi- 

 ately preceding the dilated part, be placed 

 under the microscope, it will be seen that the 

 nuclei of the secondary cells are just throwing 

 off small nucleoli, and that the parent cell is not 

 very much larger than when it burst from the 

 primary. In the same part also, little or no 

 pabulum is observed. As we proceed down- 

 wards, however, we find them increasing rapidly 

 in size ; and, at the same time, an immense 

 quantity of pabulum floating about in large 

 masses. The lower part of the tube and the 

 vas deferens are almost destitute of pabulum, 

 the cells being satiated. 



Fig. 5. Is the secondary cells of Hyas araneus from the vas 

 deferens. The walls of the parent cells, it will 

 be observed, are remarkably thin. The parent 

 secondary cells are of enormous size in this 

 species. 



Fig. 6. Represents the testicles ofCarcinus Mcenas, of the na- 

 tural size, and shortly before they have reached 

 the maximum state of developement. The portion 

 included between a a is the tubular or hepatic, 



