PLATE XVI. 



Fig. 



1. Anterior end of Tetrastemma dorsalis. a, proboscis, whose fibres have temporarily assumed 



a spiral aspect from twisting, b, tube connected with the cephalic sac of the right side. 

 Considerably magnified. 



2. Longitudinal section of the body-wall of A. lactifloreus, in a somewhat shriveled condition. 



/,/, ovisacs from which the contents have fallen. Other letters as usual. X 90 diam. 



3. Nervous plexus from the lateral trunk (n) in A.pdcher. X 210 diam. 



4. Transverse section of the anterior part of the stylet-region proper, showing the divergent 



arrangement of the oblique fibres and the position of the longitudinal series. X 210 

 diam. 



5. Three sperm-sacs (ef) with a portion of the body-wall of A. lactifloreus. X 90 diam. 



6. Spermatozoa of Tetrastemma vermicula. X 1000 diam. 



7. Spermatozoa of Tetrastemma dorsalis. X 400 diam. This drawing was made many years 



ago, and probably represents imperfectly developed bodies. 



8. Unimpregnated ovum of A. lactifloreus. a, outer coat; b 9 inner coat; c, vitellus ; 



d, " micropyle," or cicatrix-like arrangement. X 90 diam. 



9. The same ovum some hours after impregnation. The vitellus (c) is now divided into two 



portions. X 90 diam. 



10. The same ovum a few hours later. The vitellus is in four portions. X 90 diam. 



11. Ovum of the same species in the mulberry-stage. X 90 diam. 



12. Ovum just before the extrusion of the embryo. X 90 diam. 



13. Arrangement of the ova in the ovisacs of Tetrastemma vermicula. a, proboscis ; o, probos- 



cidian sheath. X 24 diam. 



14. Ovum of the same species. X 90 diam. 



15. Ovum of Nemertes gracilis after impregnation, a, outer coat; b, inner coat; c, vitellus. 



X 90 diam. 



16. The inner coat and vitellus of an ovum (of N. gracilis) at the same stage of development, 



with the relations of the spermatozoa. X 210 diam. 



17. Ovum of N. Neesii. X 55 diam. 



18. Portion of the mucous sheath with the ova of Nemertes carcinophila. X 24 diam. 



19. Ovum of the same species immediately after deposition. X 350 diam. 



20. Another ovum, about the tenth day, showing the ciliated embryo revolving therein. X 350 



diam. 



