ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 



317 



seen that a considerable, though variable, number of them are either swollen up, 

 or, more commonly, bear vesicles attached to their ends or sides (text-fig. 13). The 

 staining of the vesicles is always less intense than that of the chromosomes, and is 

 progressively fainter the more the vesicle is developed, so giving the impression that 

 the chromosome has swollen at one point, and that the chromatin is thus more thinly 

 diifused in the wall of the vesicle than in the normal part of the chromosome 

 (text-fig. 14). In the equatorial plate stage, the vesicles may either remain attached 





Text-fig. 15. 



o 



o 



(^ 



Text-fig. 14. 



Text-fig. 16. 



Text-fig. 13. — Prophase of first segmentation division of the hybrid E. acuim ? x £. esculcnius ^ . (After 



Doncaster and Gray.) 

 Text-fig. 14. — Showing the origin of vesicles from the whole or pait of individual chromosomes — 



somewhat diagrammatic. (After Doncaster and Gray.) 

 Text-fig. 1.5. — Telophase of first segmentation division of E. acutus'i x E. esculenius ,} , showing the 



elimination of four " vesicles " and the inclusion of one among the chromosomes of the right 



daughter nucleus. 

 Text- fig. 16. — Completion of first segmentation division of E. aadus'i x E. esculentux^, showing 



eliminated chromatin. 



to the chromosomes which produced them, or become separated from them ; those 

 which become separated tend to take up positions round the edge of the equatorial 

 plate, sometimes outside the spindle. The normal chromosomes, and those of which 

 the normal shape has not become much altered by vesicle production, then split 

 longitudinally in the ordinary way and begin to travel to the poles. It is possible 

 that a few chromosomes, the greater part of which have become swollen into a 

 vesicle, do not divide, but are carried entire to one or other pole. The vesicles 

 which have become separated from their parent chromosomes appear to difier in 



