Spermatogenesis iu spiders. 527 



equatorial plates of the second division. The number of autosomes 

 is thirteen in both cases. 



There seems little reason for doubting that the diploid number 

 of autosomes is twenty-six, and these together with the two accessory 

 chromsome elements and the two ctetosomes make a total of thirty 

 somatic chromosomes. 



SECOND 



SPERMATOCYTES SPERMATIDS 



iMARY SPERMATOCYTES 



SPERMATOGONIA 



Diagramm I. 



Showing the distribution of the accessory chromosome and the ctetosomes. 

 X Accessory chromosome. G Ctetosome. 



Origin and Behavior of the Accessory chromosome and 



ctetosomes. 



Accessory chromosome. 



It has been difficult to determine the origin of the accessor}^ 

 chromosome because the spermatogonia! divisions are not favorable 

 for study in Maevia vittata. But the evidence of this division together 

 with the facts afforded by the female, quod vide, makes it seem 

 probable, if indeed it does not demonstrate, that the accessory chromo- 

 some is derived from two spermatogonia! chromosomes. 



In the cells shown in Figs. 5, 6, 8 and 10, the elements marked 

 "^4." have been identified as the accessory chromosomes for three 

 reasons: a) because of their position; b) because of their size; 

 c) because of their behavior. 



The position of the accessory chromosome in all of the spiders 



35* 



