98 ETHEL NICHOLSON BROWNE 



to the observations of Benda ('02) and others, no mitochondria 

 occur in the spindle itself. In Notonecta this is true to a certain 

 extent, but a few mitochondrial fibers lie along the inside spindle 

 fibers. 



In regard to the source of the mitochondria, the evidence 

 from Notonecta leads to the conclusion that the first mitochon- 

 drial body is of cytoplasmic origin, that this becomes applied to 

 the nuclear wall, and that by an interaction of this material and 

 some of the chromatic material of the nucleus, the numerous 

 mitochondrial bodies of the later growth period are formed. The 

 mitochondria are not of nuclear origin in the sense of Ilertwig 

 for the chromatin in the nucleus and the mitochondria outside 

 are of very different appearance. But it seems quite probable 

 that their chief elaboration takes place under the influence of the 

 chromatin since this accumulates in the region where they are 

 foi-med and at the time of their formation. It seems to me proba- 

 ble that the mitochondria are merely early formed cytoplasmic 

 structures which function in the mature sperm. 



The observations on the nuclear plate in the American species 

 confirm in the main the observations of Pantel and Sinety on 

 N. glauca. The ' archoplasmic vesicles' which they find scat- 

 tered thi'ough the cytoplasm are no doubt the mitochondrial 

 spheres described above; these form part of the acrosome of the 

 sperm. The granular masses, 'material nebenkernien simple' 

 which forms the principal foundation of the nebenkern, are prob- 

 ably identical with the masses of mitochondrial filaments which I 

 have described; the fibrous nature of the masses is brought out 

 by the Benda stain. 



VII. SUMMARY 



1, The most suggestive result of the foregoing obser\'ations 

 is to show that in the case of Notonecta the change in the number 

 of the chromosomes from species to species can be explained by 

 the relations of two particular chromosomes. In N. undulata 

 these two chromosomes are always separate, in N. irrorata always 

 united to form a single body, while in N. insulata they may be 

 se))arate in the first sj^ermatocyte di\'ision, but are united in the 

 second. 



