SEGREGATION OF HOMOLOGOUS CHROMOSOMES 465 



is four (animal no. 64, plate 10) and the maximum six (animals 

 no. 69 and no. 71). Animal number 67 has, in addition to five 

 telomitic tetrads, two J-shaped tetrads, exclusive of chromosome 

 number 1, which in this instance is rod shaped, but which we see 

 from other individuals may be atelomitic. In a large group of 

 animals, then, one would expect to find a maximum of eight 

 atelomitic tetrads. This species agrees in this respect with form 

 'B' described above. Chromosome number 1 is of especial in- 

 terest ; in four cases, it is of the Stenobothrus type, in three, rod- 

 shaped, and in three, J-shaped, while in one animal (no. 70) it is 

 extremely unequal. I will have more to say later concerning 

 this point. Segregation and recombination of the dyads of the 

 heteromorphic tetrads in this species does not differ from that in 

 the larger group. 



d. Origin of a tetrad with unequal dyads. Tetrad number 1, 

 animal number 70, as mentioned above, divides very unequally 

 as shown on plate 10. Furthermore, the fiber attachment is not 

 terminal on the smaller part, which in size suggested at once 

 that it was the free arm of the atelomitic dyad of the hetero- 

 morphic form of this tetrad. A study of the late prophases gave 

 the key to the solution of the problem as to what might cause 

 such an inequality. Here we find a tetrad, normal to all appear- 

 ances, except that a pair of chromomere vesicles, 2 (so called plas- 

 masomes) described by the writer in 1913, is attached near the 

 middle of one dyad (fig. 70d, plate 11). Wenrich ('16) identified 



2 It seems desirable to qualify the term vesicle which 1 used ('13) to designate 

 these structures as chromomere vesicles or vesicular chromomeres, as the case 

 may be, in order to prevent confusion with the vesicular chromosome or chromo- 

 somic vesicles first described for the Orthoptera by Sutton ('00). 



The suggestion comes that they may stand in somewhat the same relation to 

 certain chromomeres as the chromosomic vesicles do to the chromosomes. Just 

 as given chromosomes (e.g., the accessory) have a more marked tendency than 

 others to become vesicular, these specialized chromomeres of different chromo- 

 somes may vary in this power. For example a chromomere, or granule, may 

 merely become expanded with the chromatin more or less equally distributed 

 as Wenrich ('16) has shown for one of the terminal granules of tetrad 'A' of 

 Phrynotettix. Such an expanded chromomere may or may not go a step further 

 and form a definite membrane giving a true vesicle; e.g., one of the terminal 

 chromomeres of tetrad 'B' in Phrynotettix. 



