298 



PHYLUM ARTHROrODA. 



When the branchial chamber is opened the large pyramidal gills are 

 seen, also the long sword-shaped epipodite (flabellum) of the first 

 maxillipede which seems to help the "baler," the smaller and mobile 

 epipodites borne by the second and third maxillipedes, and the broad 



^HSSB^ 5 5ssiuiiiii5 N ' 



FlG. 152. Ventral aspect of female shore crab. 

 Abd., Abdomen ; mxp.^ third maxillipede. 



scaphognathite of the second maxilla which bales the water forwards 

 and outwards. 



It must be clearly understood that the branchial chamber is entirely 

 outside of the body, being formed by the lateral extension of a hollow 

 reduplicature from the tergal region. 



The large gizzard, the enormous greyish-yellow hepatopancreas, the 

 transparent pericardium, and other organs are readily seen. 



SYSTEMATIC SURVEY OF THE CLASS CRUSTACEA 



(i) Entomostraca, lower forms. 

 They are usually small and simple. 



The number of segments and ap- 

 pendages is very diverse. 



The larva is generally hatched as a 

 simple unsegmented Nauplius. 



There is no gastric mill. 



The excretory organ is associated 

 with the second maxillae. 



(2) Malacostraca, higher forms. 



They are usually larger and more 

 complex. 



The head consists of 5, the thorax 

 of 8, the abdomen of 6 (7 in 

 Leptostraca) segments. 



The larva is usually higher than a 

 Nauplius. 



There is often a gastric mill. 



The excretory organ is usually 

 associated with the antennae, but 

 maxillary glands may be present 

 in the larvae, and may oven per- 

 sist in adults. 



