384 EDMUND B. WILSON 



ners. This view receives strong support from Montgomery's 

 recent paper on Euschistus, in which all stages of such opening 

 out are shown, and in which the process of parasynaptic union 

 is described in detail. It may be pointed out that the accurate 

 figures of Sutton ('02) from smear-preparations of Brachystola, 

 are entirely in accordance with such an interpretation, as has 

 been also indicated by Gregoire ('10). I nevertheless adopt this 

 conclusion only in a provisional way, as it is still based to large 

 extent upon indirect evidence much of which is not inconsistent 

 with the earlier and opposite conception of Paulmier. 



The facts that- have been described, especially as seen in Pro- 

 tenor, point very definitely to the conclusion that the initial stages 

 of the formation of the bivalents are passed through with as the 

 nuclei pass into the confused stage, and that they do not really 

 lose their identity in this stage but are only lost to view by their 

 looseness of structure, great extension, and intricate entangle- 

 ment. This interesting question will repay more adequate 

 study; for if my conclusion be correct it may help us to solve the 

 difficult problem of the disentanglement of the leptotene-loops 

 in the synaptic process of such forms as Tomopteris and Batra- 

 coseps (cf. p. 407). 



b. The sex-chromosomes. The history of the sex-chromosomes 

 during these stages is very easily followed throughout, particu- 

 larly in smear-preparations, and affords a complete demonstra- 

 tion of their identity with the chromatic ' nucleoli' of the growth- 

 period. In Stage h these chromosomes almost always lie close 

 against the nuclear wall, and in Lygaeus still show but little change, 

 both retaining the form of short longitudinally split rods. In 

 Oncopeltus they show a marked change, being now more or less 

 elongated into a rod-like form, often a little irregular in shape, and 

 now for the first time plainly longitudinally split (figs. 105, 106). 

 In Stage i they are regular, short, compact longitudinally divided 

 rods, essentially like those of Lygaeus save for their nearly equal 

 size. This may be studied to best advantage in smear-prepara- 

 tions, where the composition of the chromosome-groups may be 

 completely analyzed. In such preparations the total number of 

 chromosomes in Oncopeltus is nine, including seven bivalents 



