656 C. E. McCLUNG 



paper, consider Stenobothrus separately and it will be excluded 

 from general statements except as indicated otherwise. 



The spermatogonia of Stenobothrus show two important ex- 

 ceptions to the general statement already made. These are (1) 

 the number of chromosomes is 21 instead of 23 (17 in some species, 

 reported by others); (2) the point of fiber attachment may be 

 terminal, subterminal or median instead of always terminal. 

 For this latter reason the chromosomes are not always rod-shaped 

 but may also be V-shaped or J-shaped. The important thing 

 to note here is that the point of fiber attachment is a definite 

 part of the organization of the chromosomes and is constant, 

 not only for the cells of this generation but also for those of the 

 first and second spermatocyte. I have material from only one 

 individual of this species,^ with 21 chromosomes, and in spermat- 

 ogonia of this there are always 12 chromosomes with terminal 

 fiber attachment and 9 with subterminal and median. One of 

 these with median attachment is the accessory chromosome, 

 so that there are four pairs with non-terminal fiber connections. 

 The exact point at which this relation to the fibers is established 

 may vary somewhat, but as may be seen in figures 59, 60, 61 and 

 62 it is easy to distinguish these elements from the ones with 

 terminal attachment. What relation there may be between 

 the difference in number of chromosomes and the shifting of fiber 

 attachment I do not know, but the thought at once suggests 

 itself that this may be due to an altered cross segmentation of 

 a continuous spireme thread which, if there were continued 

 chromosome individuality, would produce multiple chromosomes. 

 Whatever may be the cause it is fortunate for our study that it 

 operates, because it gives ug a variation from the typical condi- 

 tions in the group which is very helpful in coming to an under- 

 standing of the movements of the chromosomes in the maturation 

 divisions. 



' I am not sure of the identification of this material. It was among a large 

 collection of specimens put up for me by a student on an early expedition into 

 western Kansas, and the specimen from which it came was not preserved. At 

 the time I made my first study of it no other form but Stenobothrus had been re- 

 ported with such chromosomes, but since then I have found them also in Chorthip- 

 pus and Chloealtis and Miss Carothers in some species of Trimerotropis. For 

 this reason I can refer it to no genus with certainty. 



