ROBERTSON: THE CHROMOSOME COMPLEX. 295 



SYHBt'LA APMIRABILIS. 



not be divided in the reduction mitosis," In reply to this the 

 results obtained on admirahilis have shown beyond a doubt 

 that the accessory is not paired in the spermatogonia. In ad- 

 dition to this it might be said that no workers upon the Or- 

 thoptera, except Montgomery himself, have ever found this 

 element to be a bivalent structure, and more than this, it has 

 been shown by Wilson ('05) that in the majority of the Hem- 

 iptera even, where Montgomery found most of his evidence for 

 a double heterochromosome, the accessory (heterotropic chro- 

 mosome) is unpaired, and Wilson believes that "it will be 

 found to be so in all" Hemiptera. Montgomery's attempt 

 therefore, to bring these two classes into harmony, was first 

 of all based upon inaccurate observations, and since that time 

 has accordingly been rendered entirely unnecessary by more 

 thorough researches. 



His final summary is that "all chromosomes and heterochro- 

 mosomes, be they paired or single in the spermatogonia, divide 

 reductionally in the first maturation mitosis, whether the di- 

 vision consists in two univalent components separating from 

 each other or a single component passing undivided into one 

 of the second spermatocytes." As far as the Orthoptera are 

 concerned it is true that in the case of the single component 

 passing undivided into one of the daughter-cells there is a 

 reduction, for only one-half of the second spermatocytes re- 

 ceive thereby this chromosome, but it is not true that all the 

 other chromosomes in the complex divide reductionally in this 

 mitosis, proof of which has been amply afforded by the be- 

 havior of the rings and crosses in Syrbula admirahilis, in Hip- 

 piscus (McClung, '00), and in the Locustidss (McClung, '02). 



INDIVIDUALITY AMONG CHROMOSOMES. 



The most live problems to-day in the field of cytology are 

 those which center around the belief that chromosomes are dis- 

 crete individual elements, which in every nucleus are constant 

 and definite morphological structures, occurring from genera- 

 tion to generation and bearing in themselves the power to 

 transmit the characters of the species. Therefore everything 

 that in any way adds to our knowledge of this subject, either 

 new or in confirmation of what has already been learned, will 

 be of interest. The chromosomes of Syrbula admirahilis are 

 well adapted for a study of these questions on account of their 

 favorable separation from each other in the metaphase figures. 



