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 o, which supplies the eyes 



Fig. 47. ANATOMY OF A CRAB. 



and the front of the body ; whilst the artery a a passes to the 

 lower and hinder parts ; at b are seen the gills of the left side 

 in their natural position ; whilst at b' are seen those of the 

 right side, turned back to show their under-surface, and to 

 disclose the lower portion of the shell, fl. At e is seen the 

 stomach, situated close behind the mouth; and at TTL 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, / 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- 



