94 ETHEL NICHOLSON BROWNE 



tion division for this figure as well as for the ring-tetrad. The 

 second division plane coincides with the second longitudinal 

 split and probably means an equation division. In the case of 

 the parallel rods, similarly, the first division separates the two 

 original components. The evidence therefore, is in favor of the 

 first division acting reductionally for all the autosomes. This 

 is not true, however, for the XF-pair, the two components of which 

 are finally separated in the second division. The fact that the 

 reduction and equation divisions are reversed in the case of the 

 XF-pair and of the A^-chromosome has been noted in many other 

 cases. With this exception and with the exception of the multiple 

 element of Mermeria (McClung '05), and possibly a few others 

 (Blackman '10), all the chromosomes are believed to undergo a 

 qualitative division at the same time. 



There is some evidence from N. insulata for Baumgartner's 

 ('04) view that the form of individual chromosomes in the pro- 

 phase is constant.. The two largest chromosomes assume a ring 

 shape, several of the large ones become crosses, one of the large 

 ones a double rod, and a small one a ring; the smallest ones could 

 not be traced. The Schreiners ('06) have also concluded that to 

 a certain point the form of a particular chromosome is constant. 

 Davis ('08) in the Orthoptera and Blackman ('10) in the rayri- 

 apods, hold the same view. On the other hand, Bonnevie ('07) 

 in Nereis and Foot and StrObell ('05) in Allolobophora, believe 

 that the form of the chromosome is merely a matter of chance. 

 Bonnevie states that rings are limited to chromosomes of a certain 

 size, and Robertson ('08) has attempted to show in Syrbula that 

 shape is dependent on size. From the fact that both very large 

 and small rings occur in N. insulata, it seems that in this case, 

 form is not dependent on size. 



VI. MITOCHONDRIA 



A. Observations 



1 . Late growth and division stages. An exhaustive study of this 

 subject has not been undertaken, but a brief treatment is given 

 because of a few observations that I have to offer. Owing to the 



