SPERMATOGENESIS OF AMERICAN CRAYFISH 593 



mic mass fragments, thereby becoming individualized around 

 many of these scattered nuclei, thus forming 'mother cells' 

 (metrocytes) from which all of the elements in the spermatogenesis 

 originate during the following season of reproduction. 



According to his account the nuclei of these primary mother 

 cells (first metrocytes) sooner or later reconstruct the chromatin 

 into a spireme. During this process they are often seen to 

 divide amitotically. When the spireme is completely formed, 

 division by mitosis makes its appearance. From now on active 

 proliferation takes place as is shown by the migration of numer- 

 ous 'mother cells' (metrocytes) from the primitive protoplasmic 

 syncitium lining the walls of the tubules, into the interior of these 

 cavities. 



The mother cells (metrocytes) multiply solely by direct division 

 (la segmentation binaire), and give rise successively to smaller 

 and smaller cells. The spermatid cells, with the exception of the 

 spermatozoa, are the smallest in the testis. 



2. Transformations of the spermatid. Gil son has given a 

 corrrect genesis of the transformations occurring in the spermatid 

 to form the spermatozoon. Within the cytoplasm of the sper- 

 matid a vacuole is formed which transforms into a hyaline 

 vesicle. This presents variations in shape and development in 

 the different species. The rest of the cytoplasm goes to form the 

 prolonged radiating arms, whose number, position and form vary 

 in the different species studied. 



The nucleus changes its spherical shape and migrates to the 

 pole opposite the vacuole. It may assume various forms, such 

 as a disc, a concavo-convex lens, a slender rod-like form, etc. 

 The contents of the nucleus becomes modified, losing its staining 

 power and appears homogeneous in aspect. A central body 

 (tigelle), was also observed in the mature spermatozoon. 



Herrmann ('09) has given a meager description of the testic- 

 ular elements of Astacus fluviatilis, Maja squinado, Eupagurus 

 bernhardus, Homarus vulgaris, Galathea strigosa, and Crangon 

 vulgaris. Most of his time was devoted to a description of the 

 development of the spermatozoa in Astacus. Herrmann, like 

 Grobben, derives the spermatogonia from the nutritive cells. 



