STRUCTURE OF CRUSTACEA. 107 
the membrane which lines the carapace and covers in the 
viscera. On the central line, at c, is seen the heart, which in 
the Crustacea is large and powerful in its action; from it 
there passes forwards the artery a 0, which supplies the eyes 
Pig. 47.— ANATOMY oF 4 CaaB. 
and the front of the body ; whilst the artery a a passes to the 
lower and hinder parts ; at } are seen the gills of the left side 
in their natural position ; whilst at 4’ are seen those of the 
‘Tight side, turned back to show their under-surface, and to 
disclose the lower portion of the shell, 77, Ate is seen the 
‘stomach, situated close behind the mouth; and at m are 
pointed out its powerful muscles, by the action of which the 
food is ground down. The bulky ovary is seen on either side 
of the stomach ; and the space between this and the edge of 
the shell is occupied by the very large liver, f o. 
100. In most of the Crustacea, however, the body is more 
prolonged. In some, as the Lobster, there is an indication of 
a division of the body into three parts, representing the head, 
thorax, and abdomen of insects ; whilst in others, as the Sand- 
