CONTENTS xv 



PAGE 



PHYLUM ARTHROPODA continued. 



Class IV. Insecta .... .571 



1. Example of the Class PeriplaM$fatamericana . 571 



2. Distinctive Characters and Classification . . 588 

 Systematic Position of the Example . . 587 



3. General Organisation . . . 588 

 Class V. Arachnida .... . 604 



1. Example of the Class Enscurpln or Buthus . . . 604 



2. Distinctive Characters and Classification . . .611 



3. General Organisation ... 613 



Appendix to the Arachnida the Pycnogonida, Linguatulida, 



and Tardigrada . . 624 



Relationships of the air-breathing Arthropoda . 627 



SECTION XII 



PHYLUM MOLLUSCA . . . 631 



Class I. Pelecypoda . . . . 631 



1. Examples of the Class Anodonta and. Unio . . 631 



2. Distinctive Characters and Classification . . 645 

 Systematic Position of the Examples . 647 



3. General Organisation . . 647 

 Class II. Amphineura . 663 



1. Distinctive Characters and Classification . . 663 



2. General Organisation . 663 

 Class III. Gastropoda . . 671 



1. Example of the Class Triton nudiferus . . 671 



2. Distinctive Characters and Classification . . 682 

 Systematic Position of the Example . 685 



3. General Organisation . . . 685 

 Appendix to the Gastropoda 



A. Class Scaphopoda . 705 



B. Rhodope . . 707 

 Class IV. Cephalopoda . 708 



1. Examples of the Class . 708 

 i. Sepia cultmta . . 708 



ii. Nautilus pompiliiis .... . . 725 



2. Distinctive Characters and Classification . . 736 

 Systematic Position of the Examples . 737 



3. General Organisation ... . . 737 

 General Remarks on the Mollusca . 751 



