VARIATIONS IN THE SIZE OF CHROMOSOMES. 22 7 



Older Nymphs. Two of them, one 26 mm. long, wing stubs 6 

 mm.; the other 33 mm. long, wing stubs 9 mm. Both were 

 collected by W. R. B. Robertson in Dickinson Co., Kansas. 



Adults. Two were furnished by Mr. Robertson from the 

 locality mentioned above. Three were furnished by the Kan- 

 sas University Zoology Department, two of them being 5. 

 americana and the other S. alutacea. The average measure- 

 ment of dried adult specimens was 44 mm. exclusive of wings. 



All material was fixed with Flemming and stained with Heiden- 

 hain's iron hsematoxylin. 



III. OBSERVATIONS. 

 i. Comparison of Chromosomes. 



(a) Chromosomes of Nymphs Compared with Those of Adults. 

 The greater size of the chromosomes of adults as compared with 

 those of nymphs is most easily seen in the first spermatocyte 

 stages, as there the chromosomes are the largest of any period in 

 their history. Great contrast in the size of chromosomes appears 

 in both metaphase and anaphase, provided the nymphs are young 

 enough. The nymphs, showing the greatest contrast were less 

 than one third grown. 



In first spermatocyte metaphase the chromosomes of young 

 nymphs occur more in the spherical or short rod form than as 

 rings or twisted rods which in adults are common. Large 

 chromosomes are usually doubled or coiled and as there are not 

 so many large ones in the nymph cells naturally the number of 

 these complicated forms is smaller. 



A large number of drawings were made as carefully as possible 

 with a camera lucida. A few of these were selected in illustrating 

 this paper. They are all typical of the material studied. 



The twelve chromosomes within a cell were numbered accord- 

 ing to their size. In almost every case the corresponding chromo- 

 somes of adult cells were larger than those of young nymph cells. 

 The exceptions to this, although few, occurred among the chromo- 

 somes of smaller size (see Plate I., Figs, i and 2, 3 and 4, 5 and 6, 

 15 and 16). In some instances there was great contrast in size 

 (see Plate II., Figs. 25 to 32). 



In first spermatocyte anaphase the same comparison holds 



