M'CLUNG : SPERMATOCYTE DIVISIONS OF THE ACRIDIDiE. 97 



the opportunity to study this object, but other members of the Gryl- 

 lid<¥ which I have examined present this element very much as it ap- 

 pears in the Locustid.e, and so I have no doubt that it also occurs in 

 Gryllotalpa. 



The work of Toyama (16) upon the spermatogenesis of the silk- 

 worm is not of a character to throw much light upon tlie methods of 

 chromosome division. His figures would indicate that the chromatic 

 elements are exceedingly small — so minute, indeed, as to be practically 

 worthless as a means of determining chromosome structure. 



It is stated, however, that the germ mother cell contains twenty- 

 eight chromosomes, and that in the tirst mitosis these divide trans- 

 versely and transmit to each of the daughter cells the same number 

 of chromatic elements. There is, as yet, no reduction in number of 

 the chromosomes, but in the mitosis of the second spermatocyte this 

 is brought about by one-half of the chromosomes going into each of 

 the resulting cells. The mitosis of the second spermatocyte is, there- 

 fore, not a division of chromatic elements, but a mere sifting apart. 



I should consider such a process as this extremely improbable and, 

 in view of the results obtained upon insect material better adapted 

 for the observation of such points, unworthy of credence unless well 

 supported by more undoubted cases. The regrettable habit of terming 

 all chromatic elements chromosomes is exemplified by this author and 

 leads to much confusion in determining the nature of the structure 

 he is discussing. 



There is some reason to believe that the body termed "nucleolus" 

 by Toyama is the accessory chromosome of other insect cells, although 

 the facts given are not sufficient to warrant a positive statement that 

 such is the case. 



V. — SUMMARY. 



1. As a result of the last spermatogonial division, the much re- 

 duced daughter cells are each provided with the somatic number of 

 chromosomes. All but one of these rapidly disintegrate and from 

 their substance produce the spireme of the first sijermatocyte. One 

 pi rsists in its original form and, assuming a peripheral position, con- 

 tinues to stain as does a chromosome of the metaphase. During 

 iiiftakinesis it is divided like the other chromosomes. This is the ac- 

 <i ssory chromosome. 



2. There is no true resting .stage between the spermatogonia and 

 sjjfrmatocyte. The prophase spireme of the spermatocyte is formed 

 immediately from the chromosomes of the spermatogonia by a disijer- 

 sii m and rearrangement of their substance. The resulting thread per- 

 sists throughout the winter and segments into chromosomes only at 



7— K.U.Qr. A— ix 1 



