NEW TYPES OF CHROMOSOME DISTRIBUTION. 155 



evidence at hand, there seems to be no doubt that Foot and 

 Strobell were in some manner misled. 



Boring ('07), in 22 species of Hemiptera homoptera, describes 

 the accessory chromosome as univalent and dividing only in the 

 second division. 



The work of McClung, Sinety and Sutton on the Orthoptera, 

 has been consistent in showing that the accessory chromosome 

 arises from a single spermatogonial chromosome. In apparent 

 contradiction to this interpretation are the results of Voinov 

 ('04) on Gryllus, Montgomery ('05) on Syrbula and Zweiger 

 ('06) on Forficula. Each of these observers describe the acces- 

 sory chromosome as arising from the fusion of two sperma- 

 togonial chromosomes and dividing in both divisions. In opposi- 

 tion to Montgomery's work on Syrbnla is the recent paper by 

 Robertson ('08) on the same genus. He seems to demonstrate 

 conclusively that the accessory chromosome is univalent and 

 divides in only one division. Randolph ("08 ) in the earwig 

 Anisolabis, describes an equal pair of idiochromosomes. May it 

 not be possible that Zweiger mistook, in Forficula, such a pair of 

 idiochromosomes for a bivalent accessory? 



Montgomery ('05) also described the accessory chromosome 

 of Lycosa, a spider, as bivalent and arising from the union of two 

 spermatogonial chromosomes. While he did not determine 

 definitely the manner of its division, he was inclined to believe 

 that it divided in both divisions, judging from the manner of its 

 formation. About the same time Wallace ('05) published her 

 account of Agalena. She figured two accessory chromosomes 

 which divided in neither division. In an attempt to unravel these 

 contradictions, Berry ('06) describes the behavior of the chromo- 

 somes in Epcira. She shows conclusively that there is an odd 

 number of chromosomes in the spermatogonia and that the acces- 

 sory chromosome is a spermatogonial chromosome which retains 

 its identity throughout the growth period and divides in only one 

 division. This makes the results in spiders consistent with the 

 majority of those in the Orthoptera and Hemiptera. 



The results of Blackmail on Scolopendra ('05) and Medes on 

 Scutigera ('05) show that the accessory chromosome in the 

 Myriapoda is a single spermatogonial chromosome, but each finds 



