32 \V. S. SUTTON. 



dimension of no value whatever. Naturally these figures can 

 make no pretensions to complete accuracy but as approximations 

 they serve to show a uniformity in the different nuclei that cannot 

 justly be ascribed to chance. It is worthy of note that the only 

 case in which a chromosome does not bear approximately the 

 same ratio as its mates to the homologous members of the other 

 two series is chromosome h of Fig. 5 ; which being hidden for 

 the most part behind the accessory, is at best a doubtful quantity. 

 ^When the ordinary chromosomes divide in the first mitosis 

 of the spermatocytes, the separation takes place along the line 

 of the longitudinal split and therefore, except that the chromo- 

 somes are joined together by pairs, differs in no respect from an 

 ordinary spermatogonial division. The accessory chromosome, 

 however, though showing a clearly-defined longitudinal split, 

 does not divide but passes entire to one pole, as Sinety ! has inde- 

 pendently observed in the Phasmidae ; and after completion of 

 the division may be clearly seen in one only of the two daughter 

 cells, where it is sharply contrasted with the partially disintegrated 



ordinary chromosomes. 



FIG. 9. 



Fig. 9. Four ordinary chromosomes and accessory from a very late prophase of 

 the secondary spermatocyte division. Each ordinary chromosome is made up of two 

 limbs connected at one end. There is no longitudinal split. 



In the prophases of the second division the chromosomes re- 

 appear in the same number and show the same size relation as in 



' Sinety, R. de(l9Oi), ' Recherches sur la biologic et 1' Anatomic des Phasmes," 

 La Cellule, T. XIX. 



