34 DUBLIN 



len Entwickelung notwendig ist, und dieses bedeutet nichts 

 anderes, als dass die einzelnen Chromosomen ver- 

 schiedene Qualitaten besitzen miissen." 



\vi Pedicellina throughout the long period of growth, from the 

 prophases of the last generation of oogonia and spermatogonia 

 through the maturation divisions, the chromosomes persist as 

 definite and distinct structures, and this in spite of the great 

 increase and subsequent condensation of the chromatin mass, 

 in many regards as marked as Riickert, '92, found in Pristiurus. 

 At no point is there any such marked disintegration of the 

 chromatin thread or any crowding together into one deeply 

 staining mass, as would make difficult the minute study of the 

 individuals. Nor is there any relation to the nucleolus such as 

 might throw uncertainty on the constitution of the chromo- 

 somes. While the latter, in their condensation, may give off 

 certain cleavage products to the substance of the ^^^ nucleolus, 

 at no point have I found any evidence for the possibility of the 

 reversal of the process. In one more regard, the conditions 

 are significant. The several chromosomes in the young 

 oocytes and spermatocytes vary considerably in size, some being 

 fully three times as large as others. Though I am unable to 

 determine any constancy in this relation of certain definite 

 chromosomes to each other, as Sutton could in Brachystola, 

 yet this proportionate diversity is obvious throughout the growth 

 period and most clear in the metaphase of the first and second 

 maturation divisions. 



[B) Reduction. 



As has been already remarked, it is in the matter of reduc- 

 tion that the most significant results of this paper were obtained. 

 Throughout the entire life cycle of somatic divisions the chro- 

 mosomes appear always in the form of V's and occur in exactly 

 this form, in the several earlier generations of oogonia and 

 spermatogonia. In the last generation, however, my evidence 

 shows unmistakably both in the Qgg and sperm that a new type 

 of chromosome makes its appearance in the form of dumb-bell 

 shaped rods in which the angle of the previous V is almost 

 completely undone, the constriction in the middle of the straight 



