SYNAPSIS AND CHROMOSOME ORGANIZATION 497 



Robertson ('16) considers the subject of synapsis in Chorthip- 

 pus at some length. His figures 163 to 180 represent about the 

 same stages as those shown on plate 1 of the present paper. 

 The evidence in the two sets of drawings is of the same general 

 nature and consists in the facts that each of the early post- 

 spireme segments is a slender filament with one longitudinal 

 split and that a second longitudinal split appears in a plane at 

 right angles to that of the first, giving rise to the tetrads. So 

 far as this evidence goes, therefore, my work, though done 

 independently serves only to corroborate his. 



In regard to the actual process of conjugation Robertson has 

 made no observations, but assumes, in accordance with the work 

 of the Schreiners ('06) on Tomopteris and Salamandra and the 

 work of Janssens ('05) on Batrachoseps, that, in the V-shaped 

 chromosomes at least, the process of pairing begins at the distal 

 ends and proceeds toward the apices of the Vs. He is further 

 led to this conclusion by finding interlocking pairs, the peculiar 

 relations of which could readily be explained on such an as- 

 sumption. He then carries the analogy over to the rod-shaped 

 chromosomes and considers that they probably also begin pairing 

 at the distal end. 



My observations, as well as those of Gerard, show that, in a 

 general way, the reverse process takes place, namely, that con- 

 jugation is initiated at the proximal end and proceeds distally. 

 In the case of the atelomitic chromosomes the evidence is not 

 quite so conclusive, but that shown in figures 2, 3, and 4, plate 3, 

 indicate that here conjugation begins at the apices of the V's, 

 and proceeds distally. However, I am inclined to believe that 

 the progress of pairing may not always be uniform along the 

 whole length of the threads, but that chance association of the 

 distal ends of a pair would result in their union, even if the 

 region between the ends and the apices had not completely 

 united. Such a condition is shown very clearly in the case of 

 chromosome A in Phrynotettix (see '16, figs. 73, plate 6, and 

 figs. 75 to 78, plate 7), and the interlocking of chromosomes 

 such as that shown by Robertson in his figures 163 and 177 

 could be explained by such behavior. 



