CHROMOSOME GROUPS IN SYROMASTES. 



2O I 



in the terminology of my former paper). By the subsequent 

 disjunction of each of these pairs the mature egg receives a and 

 b in addition to 10 other chromosomes. Fertilization of the egg 

 by a spermatozoon containing the "accessory' 1 (a -\- b} will 

 therefore give the characteristic female group (a, b, a, b -j- 20), 

 while fertilization by one that lacks a -{- b will give the male group 

 (a, b-\-2o}. For the sake of comparison two of the sperma- 

 togonial groups are reproduced in Fig. I, a, b. In the figures of 

 both sexes the chromosomes identified as a and b are made black. 

 The essential relations in both sexes are shown in the diagram, 



<f 



a 



010 



6 6 



c 



a 



88 



00 



d 



FIG. 2. Diagrams of maturation in Syromastes. a, spermatogonial chromo- 

 somes (actual number 22) ; b, c, spermatocyte-division ; d, ovarian chromo- 

 somes (actual number 24) ; e, f, maturation division (inferred). 



Fig. 2, in which a is cross-barred, b black, and the other chromo- 

 somes (of which only four are represented) are in outline. 



It is evident that, except for the different total number of 

 chromosomes in the two species, these phenomena are essentially 

 similar to those seen in Phylloxera falla.v, which likewise has two 

 " accessories " and two more chromosomes in the female somatic 

 groups (12) than in the male (10). In Phylloxera cary&caulis 

 the two " accessories " are of unequal size, as in Syromastes, but 

 the phenomena are complicated by the fact that these two chromo- 

 somes are often united in the somatic groups of the male, and are 

 apparently always thus united in those of the female. In the 

 male they are always united at the time of the spermatocyte- 



