592 NATHAN FASTEN 



special cells. Near the periphery of the tubule this connective 

 tissue presents the appearance of a meshwork, with spaces of 

 various dimensions. 



The special cells are, on the one hand, internal, situated towards 

 the center of the tubule below the connective tissue layer, and 

 on the other hand, intra-parietal, situated in the spaces of the 

 connective tissue layer toward the periphery. The former 

 elements (internal) fonn a circular layer, a sort of epithelium 

 within the tubule, while the latter (intra-parietal) elements re- 

 main scattered throughout the lacunae of the connective tissue. 

 These cellular elements, he asserts, are but two forms of the same 

 substance; both appear almost similar, multiply by amitosis, 

 and give rise ultimately to replacement cells. 



The replacement cells consist of large nuclei situated within 

 a common mass of protoplasm. They grow rapidly, become 

 round in outline and are soon surrounded by a distinct mass of 

 protoplasm, thus forming the spermatogonia (protospermato- 

 blasts). These then go to form the spermatocytes, or the so- 

 called 'deutospermatoblastes,' which in turn given origin to the 

 spermatozoa. 



Gilson ('86) made a comparative study of the spermatogenesis 

 of Astacus fluviatilis, Homarus vulgaris, Pagurus cahdus, Pagurus 

 striatus, Eupagurus prideauxii, Calibanarius misanthropus, Pa- 

 guristes maculatus, Galathea strigosa, Maja verrucosa, Xantha 

 rivulosus, Carcinus maenas, Inachus scorpio, Stenorhynchus 

 phalangium, Acanthonyx lunulatus, Dromia vulgaris, Dorippe 

 lanata and Ethusa mascarone. 



In the main, Gilson confined himself to the development of 

 the spermatogonia and to the transformations undergone by the 

 spermatids in developing into the spermatozoa. His results 

 are as follows: 



1 . Spermatogonial development. At certain periods, the tubules 

 of the testicular cavity are found to be lined with a mass of 

 undivided protoplasm, which is studded with numerous scattered 

 nuclei containing clumps of fragmented chromatin. These 

 nuclei undergo direct division throughout most of the year. 

 But when proliferation commences, the homogeneous protoplas- 



