600 CLASS X. 
antenne are short, in others very long; the external are commonly 
the longest, and in the genus Palinwrus exceed twice the length of 
the body. In some genera there are only two antenne present; 
the genus Limulus has no antennz at all. 
There are commonly two compound eyes, or two groups of 
simple eyes. The simultaneous presence of two compound eyes 
with simple eyes, so common in the winged insects, is observed in 
only very few crustaceans. In most of these there are only two 
compound eyes, which are often fixed upon a pedicle and moveable. 
The mouth of crustaceans is situated on the inferior surface of 
the anterior portion of the body. The oral organs or jaws are 
arranged in pairs and move sideways, as in manducating insects. In 
some crustaceans, however, these parts acquire a modified form, and 
compose a sucker for taking up fluids, on which these animals live. 
The description of the jaws may well detain us some moments, and 
requires a more particular survey according to the different orders. 
In the ten-footed crustaceans (lobsters and crabs) a transverse 
upper lip is present ; beneath it lies a pair of upper jaws, which are 
very hard, cut off straight at the extremity, and at the upper margin 
provided with a short feeler of two or three jomts. [Since the 
upper jaws (mandibule) in insects are without feelers, it has been 
thought that these joits do not represent a palpus, but a continua- 
tion of the pedicle of the jaws: at all events this palpus differs from 
that which occurs on the accessory under-jaws of crustaceans. | 
A thin, membranous, bifid tongue, is situated at the base of the 
upper jaws’. To it there succeed a first pair of under-jaws, which 
are membranous, divided into lobes and beset with hairs at the 
margin. Next follows a second pair of under-jaws, which are also 
membranous and haired, and may be compared with the under-lip 
of insects which has been split into two parts. ‘Then follow three 
pairs of jaws, or rather of feet changed into jaws, to be compared 
with the six feet of insects. At the outside of these accessory jaws 
a palpus is attached, which, as external division of the foot, does 
not correspond with the palpi of insects, and was named flagrum by 
Savieny. This fiagrum consists of a flat, elongated part at the 
basis, and a many-jointed filament running to a point at the end. 
1 CuvrIER calls this part sixiéme mdchoir, Leg. d’ Anat. comp. Ul. p. 304; FABRI- 
CIUS gave it the name of labiwm. 
