534 BIOLOGY. 



The Annulate animals, having branchiae and feet, are 

 the Crustacea or Grabs. 



The branchiae and feet are, of course, most largely 

 developed upon the thorax. 



Those upon the abdomen continue small, and those 

 upon the tail or sexual body dwindle in size and change 

 into other organs, such as fins, sacs, filaments, pincers. 



3262. The number five of the branchiae is also exhi- 

 bited in the feet. There are mostly five large pairs of 

 feet on the thorax, and as many small ones on the abdo- 

 men, as in the Crabs. 



On the tail they appear more dwindled in size, and 

 are frequently reduced to a smaller number. 



Each part of the body has properly five rings ; and 

 these parts being the thorax, abdomen and tail, there are 

 thus fifteen rings in all. 



In the Crabs it is distinctly demonstrated that the 

 maxillae are nothing else but feet ; there are therefore 

 for the most part, after taking into account sundry arrests 

 and coalescences, five pairs of maxillae also. 



The Crabs have usually two pairs of antennae, whose 

 signification is unknown ; one pair is probably the elon- 

 gation of the ear. 



All Branchial animals have eyes, frequently too sup- 

 ported upon articulated pedicles. 



They have a double nervous cord upon the ventral 

 surface of the body. 



They have, like the Mussels, a heart upon the dorsal 

 aspect, and arteries with veins. 



The intestine opens into the apex of the tail, and is 

 surrounded by a liver. 



The sexual parts still open for the most part on the 

 thorax, and indeed by two orifices, as in the Worms. 



There are no more androgynous or bisexual beings in 

 the present class. 



In some few the branchiae already enter the body and 

 become air-tubes, as in the Scolopendrae, Spiders and 

 Scorpions. 



The Branchial animals repeat, as being the second 



