CHEOMOSOME STUDIES 235 



late prophase, includes figures 155, 156 of Syrbula and figure 

 178 of Chorthippus; stage 'k,' metaphase, figures 157, 158 of 

 Syrbula and figures 170, 180, 182a, 182b, 183a of Chorthippus; 

 and stage 'I,' late metaphase or early anaphase, figures 181, 

 182c, 183b of Chorthippus, but none in Syrbula. 



It will be seen that, according to Janssens, the Schreiners, 

 and others, the side-by-side pairing of the leptotene chromosomes 

 begins at the distal ends. In the case of a pair of V's, it begins 

 at the free (distal) ends of the limbs of the pair. From the ap- 

 pearance of the spiremes of the autosomes of Syrbula (fig. 149) 

 and of Chorthippus (figs. 164-167, stage 'h' of Wilson, '12) — 

 where in at least two cases (figs. 149, 164) all of the.autosomes 

 are clearly visible — one is forced to admit that side-by-side pair- 

 ing has taken place and probably has proceeded from the distal 

 to the proximal part of the chromosome pair. If we grant that 

 side-by-side pairing occurs and that it begins at the distal ends, 

 then, if the process advances regularly, the last region of the two 

 threads to become approximated would be the proximal ends 

 of the rod in the case of rod chromosomes and the apices of the 

 V's in the case of V-chromosomes. In unequal tetrads formed 

 by unequal homologous chromosome pairs, in Tettigidea the 

 no. 4's (figs. 115, 120), in Acridium the no. I's (figs. 141-147), 

 in three genera of Oedipodinae, viz., Arphia, Brachystola, and 

 Dissosteira (Carrothers, '14), in Schistocerca (Hartmann, '14), 

 and in the V-rod bi-tetrad of Jamaicana-(figs. 197-199), one feels 

 very certain that reduction division is taking place. If this 

 be admitted, then in all of these cases the last region of the pair- 

 ing chromosome to be in contact with its mate is the distal end. 

 Granting this, and knowing also that the first region to pair is 

 the distal, it may be said that the proximal regions are the last 

 to pair and also the first to begin the process of disjoining. 



In a very large chromosome, such as 7-11 in figures 163 or 

 165, it is of course impossible to say whether the gaping in the 

 middle represents the end stages of the approximation of the 

 univalents in parasynapsis or the beginning stages of their 

 separation in the disjoining process. I think it is the latter, 

 because in the follicles furnishing material for figures 163 to 166 



