602 . CLASS X. 
tailed crustaceans the pectoral shield is much developed and covers 
the body beneath as the shell does above. ‘The first sternal portion 
is very large and is situated in the mid line of the body. To it 
succeed four smaller sternal pieces, which are divided in the middle 
more or less obviously since they consist of the union of two lateral 
pieces. ‘To the first piece the first pair of feet is attached, that of 
the so-called shears or claws; to the four following the four follow- 
ing pairs are united. To the basal piece of the feet the lateral 
sternal pieces (episternalia) are attached, which lie on the outside of 
the middle pieces and fill up the truncated angles between them. The 
most posterior portion of the abdomen in the decapod crustaceans is 
always obviously divided into rigs or segments, which are seven 
in number, or may be fewer from the fusion of some of the rings. 
The feet attached to these are short, commonly divided into two 
filaments; the hindmost ring bears no feet. These last abdominal 
rings are usually called the tail. In the crabs they are very feebly 
developed, and the flat tail is curved round and lies with its 
extremity turned forwards in a groove in the middle of the pectoral 
shield. 
The intestinal canal of crustaceans is short and straight, and 
thus agrees with the nature of their food, which is animal. The 
anus is situated at the extremity of the abdomen or of the tail. In 
Limulus, however, the long styliform tail is not perforate, and the 
anus is situated on the inferior surface of the second shield, in 
front of the base of the tail. So is it also with the Cirripedia, 
where the jointless tube, improperly named proboscis by some, 
represents the tail, and where the intestinal canal opens at the base 
of this tubular prolongation. In some lower crustaceans the intesti- 
nal canal is nearly of the same width throughout its whole length, 
or has in the middle or more forward an expanded part, which may 
be considered as an imperfectly defined stomach}. In others an 
obviously distinct stomach is present, which is commonly armed 
with horny spines or with calcareous teeth. In Limulus the nar- 
row cesophagus with longitudinal folds goes straight forwards and 
and form of the internal organs that lie beneath may be determined. See A. 
Broantart and A. G. Drmsmargst, Hist. nat. des Crust. fossiles, pp. 73—79, and 
DEsSMAREST Cons. gén. s. l. Crust. pp. 20—23. 
1 This is the case, for instance, in Asellus (Oniscus aquaticus L.), see TREVIRANUS 
Verm. Schr. 1. 8. 73, Tab. x1. fig. 64, &c. 
