26 Hybridization of Echinoids. 



unusual length, which may be regarded as the heterochromosome, the 

 probable explanation being that the attachment of the spindle fiber 

 was telomitic rather than atelomitic. 



In figures ll,b,c, d, and e,are shown polar views of anaphase plates; 

 b, c, d are of the first division; e is one of the daughter plates of the 

 second division. The chromosomes labeled h are those which I have 





0^9\\\ 



\^V\\ 



\ 



10 



a ^ b c 



Fig. 10, a, b, and c. Three successive sections of a first-cleavage am- 

 phiaster. One heterochromosome, 36-38. 



• • •••' !• •_ 





• ••. 





• ••' 



c 



Fig. 11a, A single section from an amphiaster in which the chromo- 

 somes were much elongated. The extreme length reached by 

 one of the chromosomes in each daughter plate may be seen 

 readily. 



116, Polar view anaphase, first division 37 chromosomes. 



lie. Polar view anaphase, first division 38 chromosomes. 



lid. Polar view anaphase, first division 37 chromosomes. 



lie. Polar view anaphase, second division 38 chromosomes, 



interpreted as the heterochromosomes, while those which are sepa- 

 rated sHghtly from each other I have regarded as autosomes. Refer- 

 ence to the figures of the lateral views of anaphase plates shows that 

 in every plate there are several chromosomes which lie rather closely 

 applied to each other. The reason for the presence of several slightly 

 elongated chromosomes in each of these polar views will be seen 

 readily when one visualizes the polar views of such sections as 8a. 

 It will be seen at once that these, and similarly oriented chromosomes 



