IO8 CHARLES V. MOKRII.L. 



In the i-j-chromosome group (Fig. 12, c) there are two very 

 large chromosomes equal in size, in place of the unpaired element 

 of the first two groups. These arc no doubt the paired idiochro- 

 mosomes. There is also a next largest pair but the w-chromo- 

 somes cannot be identified with certainty. 



A comparison of these embryonic mitoses (Fig. 12) with those 

 of the gonads (Fig. 5, a-d) shows that the 13-chromosome groups 

 are similar in the number and size-relations of their chromosomes 



FIG. 12. Protenar belfragei. Chromosome-groups of embryonic cells, a and b, 

 13-chromosome type, from the same embryo, c, i4-chromosome type, from another 

 embryo. 



to those of the spermatogonia, the 14-chromosome group, to 

 those of the oogonia. Though the results are too few to justify 

 broad conclusions, it is most probable that the embryo with 13 

 chromosomes is a male, the one with 14 chromosomes a female, 

 thus bringing Protenor in line with Archimerus, Anasa and 

 Chelinidea. 



IV. SUMMARY AND CONCLUSION. 



Among the results described in this paper, 14 those of particular 

 interest are as follows: 



1. In Archimerus, Anasa and Protenor there is an odd or un- 

 paired chromosome in the spermatogonia which in Protenor is 

 distinguishable by its size. The oogonia contain in addition to 

 this chromosome, a second chromosome of the same size. These 

 observations are in agreement with those of Wilson, Montgomery 

 and of Lefevre and McGill for the forms mentioned. 



2. The chromosomes in the reduced female groups (polar or 

 oocyte divisions) show the same relative size differences as the 

 corresponding pairs in the oogonia (particularly well shown in 

 Protenor). 



3. All the chromosomes divide in both polar divisions (proof 



J< A preliminary note giving the most important results was published in Science 

 for December 31, 1909. 



