ISO C. M. CHILD. 



different chains and in different proglottids. In one chain of M. 

 pianissimo, for example mitosis has been observed only very 

 rarely though the chain has been carefully examined ; in another 

 it was found to be much more frequent. In all cases, however, 

 amitosis is the predominant form of division in these stages. 



V 



III. Formation of the Spireme and the Growth Period. 



In the stages before spireme-formation, or as it has often been 

 called, synapsis, all the nuclei in the testes are similar in appear- 

 ance and contain a large deeply staining nucleolus with perhaps 

 a few smaller granules. 



Suddenly a part of the nuclei begin to increase in size and a 

 spireme appears (Figs. 10, A-IT,, B, PI. X.). The formation of 

 the spireme takes place in the manner described for the ovary in 

 the preceding paper of this series. The change does not appear 

 to begin in any particular region of the testis. Sometimes differ- 

 ent groups of cells in different regions of the same testis give rise 

 to a spireme while about them and between them lie others still 

 unchanged and undergoing amitosis. From the first appearance 

 of the spireme in the testes until the formation of spermatozoa is 

 completed the multiplication of the spermatogonia which remain 

 in the prespireme stage goes on, chiefly or wholly by amitosis 

 and some of the cells thus produced are continually passing into 

 the spireme stage. Consequently the stage is not characteristic 

 of any particular period of development of the testis as a whole 

 after its first appearance ; in the older testes some groups of cells 

 in the spireme stage and some groups of spermatogonia in pre- 

 spireme stages are always to be found. 



In some testes before the spireme stage appears and frequently 

 afterward some of the cells are seen to be more or less pear- 

 shaped in form with the pointed ends radially arranged about a 

 center and united by strands of cytoplasm (Figs. 10, A, 11, B, 

 PI. X.). The number of cells in a group of this kind varies from 

 three or four to eight or ten. All the cells of a group pass into 

 the spireme stage simultaneously. Whether such groups are due 

 to the persistence of cytoplasmic connections from previous divi- 

 sions or to the formation of new connections it has been impos- 

 sible to determine, but it seems possible from the varying size of 



