SEGREGATION OF HOMOLOGOUS CHROMOSOMES 473 



b. Extremes found in the group. Two individuals, number 

 6 (plate 2) and- number 62 (plate 9), have no J-shaped tetrads 

 and therefore would have only the two recognizably different 

 sorts of second spermatocytes determined by the presence or 

 absence of the accessory. Number 7 (plate 2) and 60 (plate 

 9), on the other hand, each have five J-shaped tetrads which, 

 in combination with the accessory, would give 2~. or sixty-four 

 different sorts of spermatozoa. The distribution of the J-shaped 

 tetrads in forms 'A' and 'B' as well as in the whole group, is 

 shown by the curves (text-fig. 2). The ordinates represent 

 number of individuals, the abscissae the classes of spermatozoa 

 formed. The lower broken curve represents form 'A', the 

 solid line form 'B', while the upper broken line is a composite 

 of the two. It is interesting to note that while the extremes 

 of both forms are the same and contain the same number of 

 animals, there are only four of the thirty-one members of form 

 'B' which give more than eight kinds of spermatozoa, while 

 fifteen, or practically half, of the members of form 'A' give six- 

 teen or more kinds. 



Individual number 62 is of interest on account of the large 

 supernumerary present in the spermatogonia and first sperma- 

 tocytes. There are no J-shaped tetrads in this specimen, but it 

 is possible to recognize four sorts of second spermatocytes. Of 

 two sorts with three atelomitic dyads one has eleven chromosomes 

 and the other twelve — due to the presence of the supernumerary. 

 Two sorts have four atelomitic dyads, i. e., the accessory in ad- 

 dition to the three derived from the three Stenobothrus rings 

 of the first spermatocyte. One of these has the normal number 

 (twelve) and the other thirteen, since the latter also contains 

 the supernumerary. 



Individual number 63 (plate 9) is one of the easiest to follow 

 out, since it has only one J-shaped tetrad. This, with the 

 accessory, gives two differential chromosomes, from the dis- 

 tribution of which we should expect 2? or four sorts of second 

 spermatocytes. Considering all the atelomitic dyads, including 

 those derived from the three Stenobothrus rings, we find four 



