Hybridization of Echinoids. 31 



in the upper plate in figure 21a. In figure 22, 6 or 7 chromosomes 

 have been eliminated; in figure 23, 9 or 10; while in figure 24 indica- 

 tions are that nearly all of the paternal chromosomes were in process 

 of elimination. 



The amount of chromatin in the Zwischenkorper seems to vary 

 (compare plate Ic with plate 2b), which may mean that a greater 



17 18 ^ 19 



FiQ. 17, Cidaris 9 X Lytechinus d* . V-shaped heterochromosome readily seen. X 2,400. 



Figures 18 to 24 are of anaphase plates from Cidaris eggs inseminated with Tripneustes 



sperm. They were prepared in the manner described for the figures 6 to 11 and 



reproduced at a magnification of about 2,400 diameters. 

 Fig. 18, Cidaris 9 X Tripneustes cP . A section selected because it contains all of the 



heterochromoaomes, three V's and one hook, in each anaphase plate. 

 Fig. 19. Cidaris 9 X Tripneustes d^. Section showing three V's in each plate; no hook. 



ii{'i»iiii'/ 



t hTJi/^ 



c 

 Fig. 20, a, b, and c, Cidaris 9 X Tripneustes d. Three V's, 38-35. 



amount of eliminated chromatin is included in some bodies than in 

 others. Plate 2b was drawn from a preparation in which the process 

 of destaining had been carried further than in that from which plate 

 Ic was drawn. In addition it will be seen that figure b of plate 2 

 represents a stage of completed division. Figure a of plate 2 shows 



