48 WILLIAM E. HOY. 



prophases, where the chromosomes lie at different levels, and 

 are crowded and overlapped ; (2) counting plates, one or several 

 chromosomes of which lay in an adjoining section (though this 

 does not mean that such figures are necessarily valueless) ; (3) 

 some chromosomes were torn out of the section ; (4) one or more 

 chromosomes had been cut by the microtome knife, and the 

 resulting ends or segments appeared in the next section; (5) the 

 destaining of the slide had not progressed far enough to differen- 

 tiate, one from another, some of the chromosomes lying quite 

 close together. 



Approximately one hundred groups of chromosomes from dif- 

 ferent tissues, and from a large number of embryos, have been 

 drawn and counted. The stages, extending from the incomplete 

 blastoderm stage up to about the time of hatching, which have 

 been examined, are at a period of more or less high differentiation, 

 when any chromosomal differentiation would most likely be 

 apparent, if this is a regular concomitant of cell differentiation. 

 The results so far show most conclusively that there is no such 

 differentiation in the number of the chromosomes in Anasa, and 

 that the embryos are of two classes as to their chromosome num- 

 ber, one having twenty-one, and the other twenty-two chromo- 

 somes in all the somatic cells. Moreover, the same general size 

 differences in the chromosomes may be observed in these com- 

 paratively late stages of development as are apparent in the 

 spermatogonia and the oogonia. 



The accompanying figures serve to illustrate these points. 

 The three upper figures (Figs. I, 2 and 3) are from embryos having 

 twenty-two chromosomes, and are at a stage of development 

 where the limbs are quite elongated and the embryo as a whole 

 has not shortened up. Figs. I and 2 are from the hypodermal 

 layer of the antenna, and are from the same embryo. In both 

 figures it will be noted that there are four chromosomes larger 

 than the others, though this difference in size is perhaps clearer 

 in Fig. 2. In each of the figures, again, the two w-chromosomes 

 appear. Fig. 3 is from a cell in the cerebral ganglion of another 

 embryo. These cells are much larger than any others in the 

 embryo, consequently the chromosomes are much larger. The 

 w-chromosomes are easily seen, and one pair of chromosomes is 



