ROOM IV.] NATURAL HISTORY. 83 
• 
these are different species of Squilla, the glass-like 
Alima and the Phyllosoma , which is scarcely thicker than 
a piece of paper, and nearly as transparent as glass ; they 
are found in the ocean near the equator. 
The remainder of the Crustacea ( Edriophthalma ) have 
sessile eyes. 
The order of Arthrostraca (Case 21) have a free 
head, and their body composed of a series of similar 
rings, the first seven of which are each furnished with a 
pair of feet, the following and last ones, (seven at most,) 
forming a sort of tail, ending in fins or filiform appendages. 
On the head are four antennae and a mouth composed of 
three pairs of jaws. The females carry their eggs between 
the scales in a kind of pouch under their thorax, and 
when the young are hatched, they remain attached to the 
feet or other part of the body of their mother, until they 
have acquired strength requisite to swim about and pro¬ 
vide for their own wants. They are all of a small size. 
A few are found in fresh water, and fewer are terrestrial; 
some are parasitic on other marine animals. 
This order has been divided into three sections; some, as 
the Amphipodes, have their jaws furnished with a palpus, 
while the Ltfemodipodes and Isopodes are destitute of them. 
The order of Entomostraca, on the other hand, have a 
soft head, which is merely covered with the general skin of 
the body. Both the head and the body are frequently en¬ 
veloped in a free horny or coriaceous shield, formed of 
one, two, or more pieces. The feet are all partially di¬ 
vided and ciliated. 
This order has been formed into two divisions, according 
to the structure of the mouth and the form of the feet. 
The most prominent representative of it is the King Crab 
(. Limulus ). 
They were all referred to one group by the older ento¬ 
mologists under the name of Monoculus , because they 
were believed to have only a single eye. 
The Cirripede (Cases 23 and 24,) were formerly 
considered as molluscous animals, on account of their 
being inclosed in a hard shelly case, but now that their 
history and anatomy have been studied, they prove to be 
Crustacea* nearly allied to, and indeed forming a part of 
