302 PROCEEDINGS OF THE ACADEMY OF [April, 



drawn towards the poles, the cell lengthens and with it the connecting 

 fibres. At the point at which the new cell wall will be laid down a 

 zwischenkorper of four small granules is to be seen (fig. 9). It was just 

 at this stage of telophase that Montgomery (1900) was able to demon- 

 strate that synapsis took place by an end-to-end union of homologous 

 pairs of chromosomes; in C. promethea the chromosomes were often 

 distinguishable as somewhat feathery bodies with linin connections,, 

 but they were so closely crowded, due to the small size of the cell and 

 large number of chromosomes, that it was impossible to follow the 

 process. After the separation of the chromosomes the centrosomes 

 divide and the nuclear membrane is reconstructed to form the cells of 

 the primary spermatocyte. 



2. Growth Period of the Primary Spermatocyte. — It is during this 

 period, when the cells grow but do not divide, that the chromatin under- 

 goes marked changes : it first forms a long spireme which is seen to be 

 looped on one side of the nucleus; as the looping proceeds, the chroma- 

 tin mass stains more deeply until it is impossible in ordinary prepara- 

 tions to make out anything of the spireme arrangement (fig. 12). Tnix 

 is the "synizesis" of McClung or "the contraction stage" of Wilson. 

 Since similar stages have been described by Wilson, Stevens, and a 

 number of workers on insect spermatogenesis, and since similar stages 

 appear in smear preparations, there seems little doubt but that this 

 contraction stage plays a perfectly normal part in the constructive 

 life of the cell and is not an artifact, as argued by McClung (1900). The 

 number of cells showing different stages in synizesis varies with the 

 period of development : in young pupae they ma} r occupy almost half 

 the testes, while in later stages relatively few cells may be found which 

 show this condition. What takes place during this period of intense 

 staining and contraction of the chromatin it has been impossible to 

 make out; for even when much destained little can be seen. Some 

 help has been found in smear preparations where the long thin 

 thread can be clearly seen to be formed of chromatin granules with 

 linin connections (fig. 13); though this stains much less deeply than in 

 sections, so that somewhat of its structure can be made out, yet it is 

 never definite enough to enable one to follow the steps of contraction 

 nor to determine whether conjugation of the chromosomes takes place 

 during this stage. The chromatin comes out of the contraction stage 

 by an unwinding of the condensed thread ; in a few cases this could be 

 traced as a continuous spireme (fig. 19), though usually it is made up of 

 a small number of loops which at first only partly fill the nucleus : this 

 corresponds to "stage e" or "early post synapsis" of Wilson (1905). 



