SYNAPSIS AND CHROMOSOME ORGANIZATION 501 



and consisted in a first separation (though sometimes very shght) 

 along the primary spUt, followed by a progressive separation of a 

 more pronounced nature along the plane of the secondary split. 

 When we attempt to find an analogous behavior in the atelomitic 

 chromosomes we meet with difficulties. If, however, we follow the 

 example of Robertson ('16) and consider each of the atelomitic 

 chromosomes as composed of two telomitic ones joined at their 

 proximal ends and then consider that the behavior of these com- 

 ponent rods is analogous to that described above for the telomitic 

 chromosomes, we would have to conclude that division of these 

 pairs of V's was equational. 



If we carry this idea of the compound nature of the atelomitic 

 chromosomes over to Trimerotropis, further difficulties await us. 

 Robertson uses the idea of compound chromosomes in Chorthip- 

 pus to indicate that the real number of chromosomes is 23 (cT) 

 instead of the apparent 17 (cf), and that, consequently, Chor- 

 thippus possesses the number typical of the Acrididae. If we 

 assume that the atelomitic chromosomes of Trimerotropis 

 also are compound then we should have 34 as the total 

 number of telomitic chromosomes in this particular individual 

 (see p. 506). However, if we are to consider the number of 

 chromosomes in the Acrididae to be constant or nearly so we 

 must conclude that the atelomitic chromosomes of Trimerotropis 

 are not compound and therefore we cannot carry over the analogy 

 of behavior from the possibly compound chromosomes of 

 Chorthippus. 



On the other hand the behavior of the chromatids may be 

 considered as variable, so that at one time separation in any 

 pair of atelomitic chromosomes could be along the primary 

 plane and at another time along the secondary plane. In this 

 connection, consider for a moment figure 11, plate 3. Here, there 

 are three successive 'rings' with a potential fourth at the right — 

 that is, if the two free ends were in contact, as they are at the 

 left. Each succeeding ring is in a plane at right angles to those 

 adjacent. If we may number these rings 1 to 3 beginning at the 

 left and consider the incomplete ring on the right as number 4 

 it will facilitate discussion. We might consider either plane as 



