viii CONTENTS 



PAGE 



5. Coeleuterata . . . . . .. .181 



G. Echinoderniata . . . ' . . . .183 



7. Nemertinea . 204 



8. Ctenophora .208 



9. Chaetopoda and Mollusca . . . . . .213 



10. Ascidia 229 



1 1 . General considerations and conclusions . . . 240 



12. The part played by the spermatozoon in the deter- 



mination of egg-structure 247 



13. The part played by the nucleus in differentiation . .251 



(2) The actions of the parts of the developing organism on 

 one another . .... 271 



CHAPTER V 



DKJESCH'S THEORIES OF DEVELOPMENT. GENERAL REFLEC- 

 TIONS AND CONCLUSIONS . . 279 



APPENDIX A 



On the symmetry of the egg, the symmetry of segmentation, 

 and the symmetry of the embryo in the Frog . . . .303 



APPENDIX B 



On the part played by the nucleus in differentiation . . 310 



INDEX OF AUTHOES ' . . . . . . . .315 



INDEX OF SUBJECTS . . . . . . . . 322 



ADDENDA . 341 



