CONTENTS. 



IX 



Chapter XXXIII. CEPHALOPODA^awtfwwed. 



3. The development of the external form of the embryo 



.1. Development of the embryonic rudiment through its 

 extension over the greater part of the egg with subse- 

 quent development of a yolk-sac . 



(a) Loligo .... 



(6) Octopus .... 



(c) Argonauta .... 



B. Development without actual yolk-sac 



C. Development through the formation of the embryonic 



rudiment on a limited portion of the egg with simul- 

 taneous development of a large yolk-sac 



4. The further differentiation of the germ-layers and the forma- 



tion of the organs ........ 



A. The separation of the germ -layers and the formation of 



the yolk-epithelium and the alimentary canal 



B. The covering of the body and the shell . 



The interpretation of the shell in recent Cephalopods 

 and comparison with fossil forms 



C. The sensory organs . 



The olfactory organs 

 The otocysts . 

 The eyes 



D. The nervous system . 



E. The cartilaginous skeleton 



F. The gills .... 



G. The mesodermal structures 



Chromatophores, subcutaneous tissue, musculature 

 Literature .......... 



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Chapter XXXIY. GENERAL CONSIDERATIONS 



MOLLUSCA .... 

 Cleavage and formation of the germ-layers 

 Larval form (Trochophore) 

 Derivation of the Mollusca 

 The shell and the foot 

 Origin of the organs . 

 Literature .... 



ON THE 



By K. Heidek 



Chapter XXXV. TUNICATA. 



I. Sexual reproduction .... 



1. Larvacea (Appendicularia) 



2. Ascidiae Simplices and Compositae . 



A. Oviposition, fertilisation and egg-envelopes 



Cleavage 



Formation of the germ-layers. Appearance 

 medullary tube and the notochord 

 Development of the free-swimming larva 

 External form of the body . 

 b 



B. 

 C 



D. 



of 



the 



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