ILLUSTEATIONS 



PACK 



i'lG. 



1. Eight views of the maturation of the male cells of Lepidosiren paradoxa . 5 



2. Nine stages in the transformation of a spermatid into a spermatozoon . 8 



3. Four stages in the maturation and fertilization of the egg of Crepidula 



plana ......... 10 



4. Two stages in the first division of the fertilized egg of Orepidula plana . 11 



5. Polar view of the first maturation division of the male germ cells of Alydtis 



pilosulus in order to show tetrads ...... 12 



6. Second maturation division of the male germ cells of PTOicmor icZ/rai/ei . 14 



7. Second maturation division of the male germ cells of Euschistus variolaris . 14 



8. The larva and adult female of Poriunion maenadis . . . .23 



9. The stalked larva and adult form of Anledon muUispina . . .24 



10. The larva and just-metamorphosed form of the Plaice (Phuronecles platessa) 25 



11. Vmipe egg o{ Zimulus poh/phemus. An example of a centrolecithal egg . 27 



12. The ripe egg of Stronc/yloeentrotus Uvidus. An example of an aleoithal egg 27 



13. Two stages in the segmentation of the egg of Syeandra raphanus . . 38 



14. View of the embryo of Grantia lalyrinthica in the blastula stage lying in 



the embryonic chamber of the mother . . . . .39 



15. View of the embryo of Grantia lalyrinthica in a later stage of development 



than that represented in Fig. 14 . . . . . .39 



16. Section of a portion of Grantia lahyrinthiea . . . . .40 



17. The Amphiblastula larva of Grantia lalyrinthica . . . .40 



18. Two stages in the fixation of the larva of Syeandra raphanus . . 41 



19. An early stage in the metamorphosis of the Asoon stage of Syeandra 



raphanus into the adult ....... 41 



20. A late stage in the metamorphosis of the Asoon stage of Syeandra raphanus 



into the adult condition ....... 42 



21. Longitudinal sections through the free-swimming larva of Osmrdla lolularis 



in two stages of its development and its fixation . . . .44 



22. Seven stages in the metamorphosis and fixation of 'the larva and growth of 



the young sponge of Plakina monolopha . . . . ■ . 45 



23. Two sections of the body- wall of the larva of Plakina monolopha to show 



the distinction between archaeocytes and mesenchyme . . .46 



24. Longitudinal section through the Amphiblastula larva of Esperia lorenzi . 46 



25. Longitudinal sections of the Amphiblastula larva, the just-fixed larva, and 



the young sponge of Leucosolenia varialilis . . . .48 



26. Section through a gemmule-bearing individual of ^^Aj/cJaMa Wemimi/m . 49 



27. Three stages in the formation of the gemmules of Ephydatia llemlingia . 50 



28. Two methods of formation of the blastula in Tulularia mesembryanthemum 55 



29. Formation of endoderra in Tulularia iiusemlryanthemum . . .55 



xvii b • 



