CONTENTS xr 



PAGE 



PHYLUM ARTHROPODA continued. 



Class IV. Insecta . . . . . . . 571 



1. Example of the Class Periplaneta americana .... 571 



2. Distinctive Characters and Classification 583 



Systematic Position of the Example 587 



3. General Organisation 588 



Class V. Arachnida 604 



1. Example of the Class Euscorpio 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 nodiferus 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 



IV. Cephalopoda . 



1. Examples of the Class 708 



i. Sepia cultrata 708 



ii. Nautilus pompilius 725 



2. Distinctive Characters and Classification . . . . . . 73fr 



Systematic Position of the Examples 



3. General Organisation 3 



General Remarks on the Mollusca 751 



