Studies on Chromosomes. 397 



facts. 1 In Euschistus tristigmus and Coenus delius the first divi- 

 sion is stated to show either seven or eight chromosomes (the 

 spermatogonial number being 14), but quite different interpreta- 

 tions are given of this in the two species, the conditions in Euschis- 

 tus being assumed to be due to the frequent failure of the two 

 "chromatin nucleoli" to unite in synapsis, while in the case of 

 Coenus seven of the chromosomes (including the large "chromatin- 

 nucleolus") are assumed to be bivalent, while the eighth is 

 an additional small "chromatin-nucleolus" not distinguishable 



O 



in the spermatogonia ('01, I, p. 166). In Euschistus tristigmus 

 the "chromatin-nucleoli" are stated to be of unequal size and to 

 be separated from each other without divison in the second 

 mitosis. This is evidently the same phenomenon that I have 

 described; though Montgomery overlooked the conjugation of the 

 two unequal "chromatin-nucleoli" at the end of the first division, 

 and expressly states that they are not joined together in the second 

 division. In Oncopeltus, likewise, the first division shows one 

 more than half the spermatogonial number, 16 (i. e., nine instead 

 of eight, precisely as I have described in Podisus), and this is 

 stated to result from the persistence of the two "chromatin-nucle- 

 oli" throughout the whole growth period without union; but an 

 interpretation differing from both the foregoing is here sought in 

 the assumption that each of the two "chromatin-nucleoli" is 

 bivalent, even in the spermatogonia ('01, I, p. 186). In Lygus 

 pratensis, finally, the first division shows 18 chromosomes and the 

 second 17, the still different explanation being here offered that 

 the two "chromatin-nucleoli " pass undivided one to each pole of 

 the first spindle ('01, i). Of these various interpretations only 

 the one given in the case of Euschistus tristigmus, I believe, con- 



'The first mitosis is here clearly shown to have eight chromosomes, grouped in the same way as in 

 my "Euschistus sp." and the anaphase daughter-plate of the second division is shown with seven (Fig. 

 220), precisely as in the two species I have studied. Montgomery gave the spermatogonial number, 

 correctly I believe, as 14. He nevertheless concluded that all of the eight chromosomes (seven chromo- 

 somes + i "chromatin nucleolus'') divide separately in both divisions, apparently overlooking the fact 

 that this would give the spermatozoa one chromosome too many (since he himself demonstrated that the 

 "chromatin-nucleolus"' is a modified chromosome). This account of the divisions is not modified in 

 the paper of 1901 except in the statement that "in the second maturation-division the chromatin-nucleo- 

 lus is not always divided" (p. 161), while the spermatogonial number is now given as 16. Since the 

 figures of the earlier paper show that the divisions in E. variolarius are evidently the same as in the 

 species I have examined, I think that on both these points the first account was probably more accurate 

 than the later one. 



