266 FIELD. 



EXPLANATION OF PLATE XV. 



Fig. I. Ripe living spermatozoa of Holothurioidea. K. Holothuria Poll. B. 

 Cucumaria cucumis. C. Stichopus regalts. 



Fig. 2. Ripe living spermatozoa of Crinoidea. Antedon rosacea. 



Fig. 3. Ripe living spermatozoa of Echinoidea. A. Strongylocentrotus lividus. 

 B. Sphaerechhms granularis. C. Echinus microtuberculatus. D. Echinocardium 

 cor datum (a spatangid). E. Arbacia piistiUosa. 



Fig. 4. Ripe living spermatozoa of Ophiuroidea. A. Ophiomyxa pentagona. 

 B. Ophioglypha lacetosa. C. Ophioderma longicauda. D. Ophiothrix fragilis. 



Fig. 5. Ripe living spermatozoa of Asteroidea. A. Echinaster sepositus. B. 

 Asterias glacialis. C. Chaetaster longipes. D. Astropectcji pentaca^ithus. 



Fig. 6. Diagram of testis of Ophioglypha lacetosa (Ophiurid). 



Fig. 7. Diagram of testis of Astropecten pefitacanthus (Asterid). 



Fig. 8. Diagram of testis of Cucumaria cucumis (Holothurid). 



Fig. 9. Diagram of testis of Asterias glacialis (Asterid). 



Fig. 10. Diagram of testis of Stichopus regalis (Holothurid). 



Fig. II. Diagram of testis of Brissus unicolor (Echinid). 



Fig. 12. A portion of a section of an alveolus of the testis, showing the 

 general mode of spermatogenesis ; the spermatogone {sg) being next to the ger- 

 minal epithelium, the mature spermatozoa (j-«.) in the center of the lumen of the 

 alveolus. Many of the cells are omitted for the sake of clearness. 



