146 bulletin: museum of comparative zoology. 



12. Later the chromatin collects in more or less definite masses, 

 which, in favorable cases (Chortophaga, Melanoplus), can be seen 

 to be of approximately the same number as the autosomes of spermato- 

 gonia. 



13. Each chromatic mass later becomes converted into a single 

 spireme thread, composed of a single series of chromatin granules 

 connected by linin. 



14. The spireme threads become converted into loops having a 

 polar arrangement, each loop being composed of two homologous 

 autosomes joined end to end. 



15. The polar loops later show a more or less distinct longitudinal 

 split, lliis split, howevet, does not extend to the linin, but is pro- 

 duced by each chromatin granule di\dding into two equal parts. 



16. Later the longitudinal split becomes temporarily indistinct, 

 and may entirely disappear, while the loops open out and assume a 

 peripheral position. 



17. In the early growth period the monosome becomes inclosed 

 within the nucleus, where it forms a somewhat flattened, deeply stain- 

 ing, often vacuolated element closely applied to the nuclear membrane. 



18. During the later growth period the monosome goes through a 

 complicated development, which, to a certain extent, is comparable 

 to that undergone by the autosomes during the same period. In 

 Stenobothrus and Melanoplus the monosome di^'ides into two dis- 

 similar parts, which can be distinguished up to a late stage in the pro- 

 phase of the first maturation division. 



19. Each polar loop of the growth period develops into a definitive 

 tetrad during the prophase of the first division. 



20. The bivalent autosomes, or tetrads, show the same size rela- 

 tions as the autosome pairs of the spermatogonia, and are evidently 

 formed by the conjugation of the components of each pair. 



21. In addition to the differen-ce in volume, the bivalent autosomes 

 show constant and characteristic differences in form. In general 

 several more or less distinct morphological types can be distinguished, 

 and the members of each t}^e appear to bear a constant numerical 

 relationship to each other. 



22. The first maturation diA'ision is reductional, separating ho- 

 mologous chromosomes, which united during synapsis. 



23. The second division is equational. 



24. Individual chromosomes differ in regard to the point of inser- 

 tion of the spindle fibers during mitosis, but for each chromosome this 

 point is constant throughout the spermatogonial and spermatocyte 

 divisions. 



