STUDIES ON CHROMOSOMES 67 



pale plasmosome which is considerably larger than the chromo- 

 some nucleolus. This body, particularly well shown in these 

 slides, is at once recognizable by its smooth contour, spheroidal 

 form (sometimes double, as in fig. II) and pale yellowish color 

 after the hsematoxylin, and it forms a striking contrast to the 

 intense blue-black of the chromosome-nucleolus. Nuclei in 

 which all five bodies the three small chromosomes and both 



diploid nuclei. This assumption which is doing much to confuse the whole sub- 

 ject may accord with the facts in certain species, but certainly is not generally 

 true. Much of the recent work in this field, as well as some of the earlier (e. g., that 

 of McClung '00, and Button '00) goes to show that in many species it is only in 

 the growth-period of the spermatocytes that this chromosome forms a chromosome 

 nucleolus, not in the diploid nuclei of either sex. Such seems to be the case in all 

 the Hemiptera that I have studied. In these animals the accessory chromosome, 

 or its homologue the large idiochromosome, first assumes the nucleolus-like con- 

 dition in the post-spermatogonial stages, when its origin from an elongate chromo- 

 some may in some species readily be followed step by step, as I have shown in 

 Lygaeus ('056) and Pyrrhocoris ('096). In the spermatogonia of these animals 

 this chromosome does not differ visibly in behavior from the others and cannot 

 be seen in the resting nuclei. 



Several years ago, in two successive papers ('05a, '06) I described and commented 

 on the interesting fact that in the female this chromosome (and its fellow, when 

 present) seems in some species not to assume a nucleolus-like condition in the 

 synaptic stage and early growth-period of the oocytes. Since some doubts on 

 this point were raised in my own mind by the later work of Stevens ('06) and Gut- 

 herz('07)I am now glad to have the very positive confirmation of my results given 

 by the work of Foot and Strobell ('09) on Euschistus (one of several forms I had 

 examined). This confirmation must have been made without knowledge of my 

 previous work, since the latter is referred to in neither text nor literature list, and 

 the supposedly new facts are made the main basis for renewed attack upon my 

 general conclusions. On the other hand Buchner ('09a) has recently found in the 

 synaptic or "bouquet" stage of the oocytes in Gryllus a nucleolus-like "accessory 

 body" which he believes to be of the same nature as the accessory chromosome 

 of the male, though its history in maturation was not followed out, nor is other 

 proof of the conclusion given. 



It is of some psychological interest to find Buchner on the one hand and Foot 

 and Strobell on the other disputing my conclusions regarding sex-production on 

 diametrically opposing grounds, the first-named author because (as he believes) 

 a chromosome-nucleolus is present in the oocyte-nucleus, the last named because it 

 is absent(\). In what way either of the mutally contradictory arguments inval- 

 idates or weakens my conclusions I am not yet able to perceive, nor need we here 

 consider the contradiction in the data; but it is interesting to observe how each 

 of the arguments goes awry by reason of the confusion regarding the chromosome- 

 nucleolus, referred to above. Foot and Strobell, for example, argue that because 



