NEW TYPES OF CHROMOSOME DISTRIBUTION. I 2J 



in it are the three differential chromosomes as densely staining 

 compact bodies (Fig. 2, /<"). In the prophase of the first divi- 

 sion, the plasmosome disappears and the differential chromosomes 

 remain (Fig. 2, L). 



Rocconota annulicornis Stal. 



With the exception of the size relations of the differential 

 chromosomes, we find practically the same conditions in this 

 form as in Fitchia. The spermatogonial cells (Fig. 3, A and 

 B) show 27 chromosomes. Unfortunately no good female 

 groups were present in my material, but since the relations are 

 so similar to those found in Fitchia, there seems little doubt but 

 that it contains one more chromosome than the male. In the 

 first division, metaphase plate (Fig. 3, C and D), are 15 chromo- 

 somes, three of which are distinctly smaller than the remaining 

 twelve, and which prove to be the differential chromosomes. All 

 divide equally in this division. The characteristic regrouping 

 in the second division again occurs. The 12 larger chromosomes 

 form an irregular ring with the triad group, made up of the three 

 differential chromosomes in the center (Fig. 3, G and H, side 

 views of the second division, metaphase). Here all three differ- 

 ential chromosomes are practically of the same size. The chro- 

 mosomes in the ring divide equally, while those of the triad 

 group separate as in Fitchia, so that two pass to one pole and one 

 to the other. The two classes of spermatozoa thus produced, 

 are essentially similar to those of Fitchia, and are respectively 

 male and female producing. Fig. 3, / and ] , are two anaphases 

 taken from the same spindle which show the unequal distribution 

 of the chromosomes, 14 passing to one pole and 13 to the other. 



Throughout the growth period, from shortly after synapsis 

 to the prophase of the first division, there is present a distinct 

 pale plasmosome, in which are embedded the three differential 

 chromosomes (Fig. 3, K and L). The exact stage in which the 

 plasmosome and chromosomes make their appearance could not 

 be determined. Fig. 3, M, represents the prophase of the first 

 division, where the plasmosome has disappeared. The differ- 

 ential chromosomes stand out in marked contrast to the looser 



