Vlll CONTENTS. 



PAGE 



CHAPTER XXXI. SOLENOCONCHA. By E. KORSCHEI/T ... 88 



1. Cleavage and formation of the germ-layers .... 88 



2. The development of the form of the larva .... 90 

 8. The transformation of the larva into the adult ... 95 



Literature 98 



CHAPTER XXXII. GASTROPODA. By E. KORSCHELT . . . 99 



1. Oviposition and character of the egg-capsules and the egg . 101 



2. Cleavage and formation of the germ-layers .... 106 



3. The formation of the germ-layers 113 



The mesoderm 117 



4. The rise of the larva and its relation to the adult form . .123 



The ontogeny of Patella . 123 



The Trochophore stage 127 



The Veliger stage .131 



The development of Paludina 134 



The primitive kidneys 136 



The shape and transformation of the blastopore . . . 140 



Considerations relating to the asymmetry of the Gastropoda 143 



5. The development of the external form of the body in the 



different divisions of the Gastropoda .... 148 



A. Prosobranchia . ... 148 



B. Heteropoda 153 



C. Opisthobranchia 158 



D. Pteropoda 166 



Thecosomata 167 



Gymnosomata 171 



E. Pulmonata 174 



The ontogeny of the Sty lorn atophorous terrestrial 



Pulmonates 184 



6. The formation of the organs 187 



A. The shell 187 



B. The nervous system . . 188 



C. The sensory organs 196 



The eyes 196 



The otocysts 199 



The osphradium 199 



D. The pedal glands 200 



E. The alimentary canal 200 



F. The gills 208 



G. The differentiation of the mesoderm-rudiment, the 



development of the body-cavity, the nephridial and 



circulatory systems 209 



H. The genital organs 217 



Literature 224 



CHAPTER XXXIII. CEPHALOPODA. By E. KORSCHELT . . . 235 



1. Oviposition and the constitution of the egg .... 236 



2. Cleavage and formation of the germ-layers .... 240 



