54 



INTRODUCTION TO CLASSIFICATION. 



communicates, by valvular apertures, with the surrounding 

 venous sinus the so-called " pericardium." 



The Crustacea vary through such a wide range of organiza- 

 tion that I doubt if any other anatomical proposition, in addition 

 to those which I have mentioned, except the presence of a 

 chitinous integument and the absence of cilia, can be enunciated, 

 which shall be true of all the members of the group. 



Fie. 27. 



Fig. 27. Amphithoe, an amphipodous Crustacean. Lateral view (A), longitudinal and ver- 

 tical section (B), detached appendages and stomach (C, D). The numbers I' to XX' 

 indicate the appendages of the corresponding somites, r. Rostrum, t. Telson. Ib. 

 Labrum. st. Roof of the head, or cephalostegite. os. Oostegite. Br. Branchiae. 

 Stomach opened from above (D) , and viewed laterally (C). a, b, c. Different parts of the 

 armature. 



