THE ACCESSORY CHROMOSOMES. 55 



themselves, and persist as the two small chromosomes of the 

 spermatogones. These then undergo a pseudo-reduction and 

 form a tetrad which is unable to complete the second sperma- 

 tocyte division." 



40. My own early views concerning the accessory chromosome,, 

 as manifested in the Locustida,% may be found expressed in the 

 following quotations from my first paper ('99) upon the subject : 



41. " As it first appears in the spermatogonia of Xiplddium 

 fasdatum, there would be no hesitation in calling it a nucleolus 



except for its unusual situation on the surface of the nuclear 

 vesicle. It is a small, irregularly rounded body, and lies im- 

 mediately under the nuclear membrane. Before the division 

 figure is established, however, it takes on the form of a thread 

 which becomes ' U '-shaped. Still further contraction ensues, 

 and by the time of the metaphase the thread has become very 

 short and thick and is bent in the middle with an obtuse angle 

 so as to resemble a boomerang. At this time, it may be ob- 

 served lying at one side of the circle of chromosomes arranged 

 in the equatorial plate, and plainly distinguishable from them by 

 reason of its greater length. From the pole the chromatin ap- 

 pears as a broad, fenestrated plate, and the accessory chromo- 

 some is indistinguishable from the ordinary ones. Because of the 

 rapidity of the division none of the anaphases are to be seen, but in 

 the telophases the ordinary chromosomes of the cell may be 

 seen grouped in the typical manner at the two ends of the spindle, 

 while extending down towards the equatorial plate from each 

 mass is a half of the boomerang-shaped body which has been 

 divided longitudinally in the same manner as the ordinary 

 chromosomes. 



42. " In the resting stage of the spermatocyte that succeeds 

 the appearance just described, the accessory chromosome again 

 appears as it did in the resting stage of the spermatogonia, and 

 would easily be taken for an ordinary nucleolus. Soon, how- 

 ever, it commences to assume a thread-like form which finally 

 results in the production of a long 'U '-shaped body, a form that 

 is retained during the greater part of the spireme stage. In this 

 condition it lies at the surface of the vesicle and stains in its usual 

 intense manner. Concurrently with the formation of the ' rings ' 



