134 D. H. TENNENT. 



Explanation of Plate 1. 



All of the figures were drawn with the aid of a camera and Zeiss compensation 

 ocular 12 and 2 mm. Apochromatic oil immersion objective. They were enlarged 

 two diameters with a drawing camera and have been reduced to one half in 

 reproduction. 



Fig. I. Toxopneustes tgg'^(^ Toxopnetistes s^trm. Equatorial plate. Polar view. 



Fig. 2. Same as Fig. i. 



P"lG. 3. I\Ioira egg X Moira sperm. Eq. pi. 



Fig. 4. Toxopneustes egg X Moira sperm. Eq. pi. 



Fig. 5. Same as Fig. 4. 



Fig. 6. Arbacia eggyc^ Ai-bacia sperm. Eq. pi. 



Fig. 7. Arbacia egg X Moira sperm. Eq. pi. 



Fig. 8. Same as Fig. 7. 



Fig. 9. Toxopneustes egg X Moira sperm. Segmentation nucleus with centro- 

 some undivided. Extra sperm nucleus with aster divided. 



Fig. 10. Toxopnetistes egg X Moira sperm. Segmentation nucleus with centro- 

 some divided. Extra male nucleus, with its aster divided, in contact with segmenta- 

 tion nucleus. 



Fig. II. Toxopiieiisles eggyC^ Moira i^trra. Segmentation nucleus with centro- 

 some divided. Fibers from aster of extra sperm nucleus extending into the segmenta- 

 tion nucleus. 



Fig. 12. Toxopnetistes egg X Moira sperm. Segmentation nucleus and extra 

 sperm nucleus lying side by side and both preparing for division. 



