lO-j- CHARLES V. MORRILL. 



very clear preparations. Many more could have been shown, but 

 it seemed needless to multiply the number of figures. 12 



A comparison of the male groups (Fig. 8, a-h) with the female 

 groups (Fig. 9) shows clearly that in the- former there are three 

 chromosomes larger than the rest, while in the latter there are 

 four such elements. These size relations are the same as those 

 in the spermatogonia and oogonia respectively (vid. page 89). 



$ 



V. r n^f/ 



*~P e *QsS 





FIG. 9. Anasa tristis. Chromosome-groups of embryonic cells, 22-chromo- 

 some type, all from the same embryo. 



Accordingly, one of the large chromosomes of the male groups 

 must be the unpaired idiochromosome and two of the large chro- 

 mosomes of the female groups, the paired idiochromosomes. The 

 m-chromosomes appear as constant elements in both groups and 

 are usually more, elongated than in the germ-cells, a feature which 

 is common to all I he chromosomes. Apart from the largest and 

 smallest elements, this elongated condition makes it impossible to 

 pair off the remaining chromosomes with any degree of certain i \ . 



12 A11 the figures were drawn with camera lucida, Zeiss apochromat. 2 nun., 

 compens. oc. 12. With the exception of Plates I. and II., they were again rnl.r 

 with the camera and subsequently reduced in reproduction one-half, giving a final 

 magnification of 2,650 diameters. The magnification of Plates I. anil II.. is i.sv.s 

 diameters. Achromatic structures, except those of Plates I. and II.. havr Inn. 

 represented semi-schematically. 



