EXPLANATION OF THE PLATES. xxi 



Fig. 4. This figure shows the adult seminal secondary cells from the 

 dilated parts 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 accordingly great numbers of the secondary 

 cells, in all stages of development, are constantly found here. 

 If a small quantity of the seminal fluid from that portion of 

 the testicle immediately preceding the dilated part be placed 

 under the microscope, it will be seen that the nuclei of the se- 

 condary 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 ob- 

 served. As we proceed downwards, 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 desti- 

 tute of pabulum, the cells being satiated. 



Fig. 5. The secondary cells of Hyas araneus from the vas deferens. 

 The walls of the parent cells are remarkably thin. The 

 parent secondary cells are of enormous size in this species. 



Fig. 6 Represents the testicles of Carcinus mcenas, of the natural size, 

 and shortly before they have reached the maximum state of 

 development. The portion included between a a is the 

 tubular or hepatic, that between 6 b is the dilated or gastric. 

 The vasa deferentia are not seen in this species so well as in 

 Hyas araneus, Fig. 8, c c. It is in the gastric division that 

 the pabulum lies in such quantities. 



Fig. 7 Is the internal or sheathed portion of the external organs of 

 Cancer pagurus ; proximal extremity. 



Fig. 8. Testes of Hyas araneus. a a. Tubular portion. 6 &. Follicular 

 portion, c c. Vasa deferentia. 



Fig. 9. External organs of Cancer Pacjurus. a. Is the internal or 

 sheathed portion in situ. b. Is the sheath or external portion. 



Fig. 10. External organs of Hyas araneus. A. Sheath. B. Sheathed 

 portion. 



PLATE VIII. page 431. 



Fig. 1. First stage of development of secondary seminal cell of Gala- 



thea strigosa. 

 Figs. 2, 3, 4. Second, third, and fourth stages of development of the 



secondary cell. 

 Figs. 5, 6, 7, 8, 9, 10, 11, 12, 13. Various stages of development of 



the secondary cell of lobster. 

 Figs. 14, 15, 16, 17. The same treated with acetic acid. 



