3O W. S. SUTTON. 



which, as we have seen, projected into a common chamber of the 

 nucleus. To such a conclusion additional weight is added by 

 the occasional finding of telophases of the last spermatogonial 

 generation which actually shows such a fusion (Fig. 8). 



Fir,. 8. 



Fir.. 8. Telophase of secondary sperm atogonium of the last generation showing 

 synapsis. Only a few of the chromosomes are shown and as in Fig. 4 ; to avoid con- 

 fusion the sacculations are drawn only to the point where they cross one another. 



The four parts of each spireme, marked off by the longitudinal 

 split and the line of fusion, may be traced through all the pro- 

 phases up to the metaphase, where they are clearly seen to 

 become the four parts of the tetrad. These facts seem to me to 

 leave no escape from the conclusion that in the completed tetrad 

 the longitudinal split represents merely the usual division of a 

 chromosome into equivalent chromatids ; but the transverse mark- 

 ing separates two spermatogonial chromosomes which have conju- 

 gated end-to-end in synapsis} 



Notwithstanding the fact that no continuous spireme is formed, 

 the various spiremes of the larger group (16 in spermatogonia, 8 

 in spermatocytes) in any nucleus are at any given period always 

 of approximately the same diameter and the same degree of con- 

 centration. Their respective lengths may therefore be taken as 

 a measure of their respective volumes, and accordingly the longer 



1 Cf. Montgomery, T. H., Jr. (1901), " The Spermatogenesis of Pcripatus (Peri- 

 fatopsis) Balfouri up to the Formation of the Spermatid," Zool. Ja /i >-/>., XV.; also 

 "A Study of the Chromosomes of the Germ Cells of the Metazoa," Trans. Amer. 

 Phil. Soc., Vol. XX. 



