CHROMOSOME-GROUPS OF METAPODIUS AND BANASA. 307 



When the ^-chromosome is present it sometimes (in about 20 

 per cent, of the cases tabulated) lies free--z. e., not connected 

 with any other in either division and after dividing in the first 

 division, passes undivided to one pole in the second (Fig. i,g). 

 In most cases it is in the second division attached to one or the 

 other of t/ie idiochronwsonies and passes with it, undivided, to one 

 pole (Fig. i, h, i, /). In either case one pole receives 1 1 chromo- 

 somes and one 12, as may clearly be seen in polar views of the late 

 anaphases which show both daughter-groups of chromosomes in 

 the same spindle. Four classes of spermatozoa are accordingly 

 formed in this type, which correspond to those described in 

 Banasa ealva. Designating the ordinary chromosomes or " allp- 

 somes " as " 0," the large and small idiochromosomes respec- 

 tively as "/'" and "/," the w-chromosome as "m" and the 

 .y-chromosome as " s" the classes are as follows : 



* 



(1) 9 O + I + m + s = 12, 



(2) 9 + I + in = 11, 



(3) 9 + / 4- ;// + s = 12, 



(4) 9 + i + in =-.11. 



So far this is identical with the conditions described in Banasa 

 calva except that in the latter case the unpaired chromosome fails 

 to divide in the first division but divides in the second, while the 

 reverse condition obtains in Metapodius. But there is now an 

 important difference to consider which involves the most interest- 

 ing phenomenon that occurs in this form. In Banasa calva the 

 four classes are equal in number. In Metapodius, at least in cer- 

 tain individuals, this is not the case ; for the ^-chromosome shows 

 a marked tendency to couple with the small idiochromosome 

 rather than the large, which produces an excess of spermatozoa 

 in which these two chromosomes are associated. It is somewhat 

 difficult to secure adequate data, since the nature of the coupling 

 can, as a rule, only be determined with certainty in side views of 

 the middle anaphases. Out of 34 clear cases (taken from two 

 individuals) the ^-chromosome is coupled with the small idio- 

 chromosome in 24 and with the large in io--/. e., in about 70 

 and 30 per cent, respectively, a ratio which may very likely be 

 somewhat altered with a larger series of data. Of the four 

 classes, accordingly, 2 and 3 are more numerous than i or 4. 



