THE "ACCESSORY CHROMOSOME' IN EPEIRA. 



EVIS HOWARD BERRY. 



INTRODUCTION. 



The problem involved in the following paper was suggested to 

 me in August, 1905, by Professor E. B. Wilson, in view of the 

 apparent contradiction that occurs between the insects and spiders 

 in regard to the origin and behavior of the so-called " accessory 

 chromosome." 



In many of the Orthoptera (Acrididse ('oo), and Locustidae 

 ('02) McClung ; Acrididae ('oo and '02) Sutton ; and Phasmidae 

 ('01) de Sinety) the accessory chromosome has been found to be 

 derived from a single, univalent spermatogonial chromosome, 

 which splits longitudinally during the growth period, the two 

 halves passing bodily to one pole in the first division. In the 

 second division, however, these two halves were found to sepa- 

 rate, being distributed equally to each of the resulting spermatids. 

 Professor Wilson in his " Studies on Chromosomes," II. ('05), 

 gives a general account of the accessory chromosome in the 

 Hemiptera, which is consistent with the preceding results in the 

 Orthoptera, though not identical. He says, p. 533 : " The 'ac- 

 cessory ' or heterotropic chromosome is certainly in most Hemip- 

 tera and I believe will be found in all unpaired in the 

 spermatogonia, and its behavior is throughout that of a univalent 

 body. . . . This chromosome divides in only one of the matura- 

 tion divisions, passing undivided to one pole of the spindle in the 

 other. The latter division is usually the second (Pyrroclwris, 

 Anasa, Protenor, etc.), but in Archimerus and Banasa it is the 

 first. In either case one half the spermatozoa receive one more 

 chromosome than the other half." 



Opposed to the foregoing conclusions are those of Montgom- 

 ery ('05), obtained from a study of Syrbula (one of the Acri- 

 didae), and of Lycosa, a spider. In these two unrelated forms he 

 found the accessory chromosome of the growth period to be 

 formed by the union of two univalent spermatogonial chromo- 



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