575 



While in the majority of cases the odd chromosome appears as 

 a single large elongated, often slightly curved body, not infrequently 

 it exhibits a double or more often a tripartite structure as shown in 

 Figs. 6, 7, 9, 12 and 13, which causes one to believe that in reality 

 it is a compound chromosome. Furthermore, one of the components 

 is at times so loosely attached as to lead to the supposition that we 

 are dealing here not only with the odd or accessory chromosome pro- 

 per buth with an additional body which has become closely associated 

 with it and often, indeed, forms an indistinguishable part of it. The 

 body in question is possibly comparable to a „supernumerary" as 

 described by Wilson^) and others, for various insects. This sup- 

 position seems to be the most reasonable one that presents itself to 

 account for such conditions as are figured in Figs. 9, 10, 11 and 12. 

 In Fig. 9 a very distinct tripartite (or bipartite and single super- 

 numerary) lies well to the right of the main plate of chromosomes and 

 is connected by a spindle fiber to but one pole of the spindle. Fig. 11 

 represents a not unusual condition in which the tripartite has become 

 separated into a curved rod-like portion and a smaller round chromo- 

 some which is presumably the . supernumerary-like component. In 

 Fig. 10 a much rarer example is shown in which the rod-like portion 

 and the small component lie on opposite sides of the equatorial plate 

 and will presumally go to opposite poles; the spindle is seen at a 

 considerable angle and not directly from the side. In some few in- 

 stances a round chromosome, to all appearances the loosely attached 

 round component of the tripartite was observed alone at or near one 

 pole without any trace of its larger rod-like accompanist. Whether 

 the latter was simply delayed in the equatorial plate or whether it 

 was entirely missing could not be determined. In exceptional cases 

 ten chromosomes were counted and it may be supposed therefore, 

 that sometimes though rarely the component of the odd is set apart 

 in even the equatorial plate stage. 



While in the above description the divided condition of the odd 

 has been emphasized, the fact should still be borne in mind that per- 

 haps in the majority of cases it appears more as a solid elongated 

 mass and that while it may consist of three components this is by 

 no means evident in every case. Sometimes it can not be distinguished 



1) E. B. WiLson: Note on the Chromosome Groups of Metapodius 

 and Banasa. Biol. Bull., Vol. XII, No. 5, 1907. — Id., The Super- 

 numerary Chromosomes of Hemiptera. Report of May Meeting N. Y. 

 Acad. Sei., Science, N. S., Vol. XXVI, p. 677, 1907. — Id., Studies 

 on Chromosomes. Journ. Exp. ZooL, Vol. VI, No. 2, 1909. 



