CHA PT HE ¥- 
CRUSTACEA (CONTINUED) : MALACOSTRACA: LEPTOSTRACA — 
PHYLLOCARIDA : EUMALACOSTRACA: SYNCARIDA — ANAS- 
PIDACEA : PERACARIDA——MYSIDACEKEA—CUMACEA——ISOPODA 
-—AMPHIPODA: HOPLOCARIDA—STOMATOPODA 
SUB-CLASS IIL—MALACOSTRACA. 
THE Malacostraca are generally large Crustacea, and they are 
characterised by the presence of a definite and constant number 
of segments composing the body. In addition to the paired eyes 
we can distinguish two pairs of antennae, a mandibular segment, 
and two maxillary segments composing the head-region proper ; 
there then follow eight thoracic segments, the limbs belonging 
to the anterior thoracic segments being often turned forwards 
towards the mouth, and modified in structure to act as maxilli- 
pedes, while at any rate the last four are used in locomotion and 
are termed “pereiopods.”! The abdomen is composed of six 
segments, which typically carry as many pairs of biramous 
“pleopods,” and the body terminates in a telson. Not counting 
the paired eyes or the telson, there are present nineteen segments. 
The excretory organs in the adult open at the bases of the second 
antennae, and are known as “green glands,” but in the larva 
maxillary glands may be present homologous to those which per- 
sist in the adult Entomostraca. This is the typical arrange- 
ment, but sometimes the maxillary glands persist in adult 
Malacostraca, e.g. Nebalia, Anaspides, and some Isopods. 
The hepato-pancreatic diverticula are directed postericrly, and 
not anteriorly as in most Entomostraca, and the stomach is often 
furnished with chitinous teeth and ridges forming an elaborate 
gastric mill, especially in the larger Decapods. 
1 The term pereiopod is applied to those thoracic limbs which are used in 
locomotion, and are not specially differentiated for any other purpose. 
I1O 
