A STUDY OF SOMATIC CHROMOSOMES. 1 67 



found in the spermatogonia. Again, in all the figures the small 

 y-chromosome is very conspicuous. The x-chromosome is here 

 undoubtedly the next smallest in size, since this chromosome 

 has no homologous mate. All the chromosomes show the typical 

 elongate and more or less slender form characteristic of the 

 Coleoptera. There do not seem to be any special peculiarities 

 shown by the seven pairs of mesochromosomes, ranging between 

 the macrochromosome pair and the xy pair, other than that they 

 fall into a graded series according to size. 



Plates from embryos containing no very small y-chromosome, 

 but apparently having the small x-chromosome paired, are shown 

 in Figs. 5-8. All these figures again show the large pair of 

 macrochromosomes, and a series of seven paired mesochromo- 

 somes graudally diminishing in size. In none of the figures is 

 there a small rounded y-chromosome, but in its place there is 

 another the size of the x-chromosome. 



It has, therefore, been possible to demonstrate that in Epi- 

 lachna, where the male has an x-y pair in the spermatogonial 

 complex, the embryos fall into two classes as regards their chro- 

 mosome content, one class containing an xy pair, and the other 



2 x's. 



RECORD OF COUNTS OF CHROMOSOMES IN Epilachna. 



STAGE I. 



Cleavage Mitoses, xy Type. 



Embryo. No. of Chromosomes. No. of Counts. 



1 18 I 



2 18 8 



3 18 2 



4 18 i 



5 18 2 



6 18 2 



Total . . . . 16 



Cleavage Mitoses. 2.x Type. 

 Embryo. No. of Chromosomes. No. of Counts. 



1 18 I 



2 l8 2 



3 18 i 



4 18 r 



5 18 i 



6 18 3 



Total .... 9 



