SUTTON : SPERMATOGONIAL DIVISIONS IN BRACHYSTOLA MAGNA. U{f 



seems to be constant, as intimated by Panlmier and McGregor. The 

 number is probably seven, which would give 256 cells to the cyst of 

 early spermatocytes, since secondary spermatogonia tirst appear in 

 pairs as a result of the last division of a primary spermatogonium. 



Seventh, the method of origin, as already described for this object 

 would argue against any attachment of the cysts to the walls of the' 

 folhcles, as described by St. George and as suggested by Montgomery. 



II. ne Accessory Chromosome. — It has long been customary 

 with observers to classify all the solid elements of the cell nucleus 

 under three heads, viz.: Chromosomes, fibers of various kinds, and 

 nucleoli. 



The tirst two have been restricted to similar structures in the dif- 

 ferent forms, so that in regard to them no great confusion has arisen - 

 but m regard to the latter such is not the case. The term " nucleolus '' 

 has had to serve for everything not falling directly under the other 

 heads, m the opinion of the investigator : and truly it has with a 

 greater or less degree of efficiency, covered a multitude of' errors 

 The most divergent bodies have been included under the same term 

 regardless of behavior, staining reaction, or, in fact, of anything else' 



One of these much-neglected elements is that which in this paper I 

 have called (after McClung ) the "accessory chromosome." This most 

 interesting structure, which I have reason to believe present in the 

 sperm-cells of all insects, has been noted by a number of authors as 

 behaving differently from the ordinary nucleolus, and has been vari 

 ously designated as "nucleolus.-' "secondary nucleolus," "chromatin 

 nucleolus," and recently, by Paulmier. as the "small chromosome " 



It IS most conspicuous in the growth stage of the spermatocyte 

 and consequently has been more frequently noted here than in the 

 spermatogonia. 



In Brachiistola, the accessory chromosome appears probably in the 

 first, and certainly in the third, secondary spermatogonia! division and 

 goes through precisely the same changes in each cycle up to the last 

 _ It may occasionally be distinguished from the other chromosomes 

 m the metaphase and anaphases by its granularitv and greater length 

 though it always divides like the others, and in the actual process of 

 division, as a rule, is indistinguishable from them. In the telephase 

 It constructs its own membrane just as do the others, but soon be- 

 comes sharply contrasted with them by the deposition of its chromatin 

 in a diffused condition upon the inner surface of its vesicle (vesicular 

 chromosome), and also by the fact that from this point to the follow- 

 ing metaphase the cavity of its vesicle remains distinct from that 

 formed by the junction of all the others. In these stages the vesicle 

 of the accessory chromosome may lie on any portion of the nuclear 



