238 SUPPLEMEXT 



neath this testa of very distinct segments, and these segments 

 themselves are composed of several pieces. The under part 

 of the body in the brachyurous decapods presents a surface 

 more or less extensive, which may be compared to the breast- 

 plate of the tortoises. Its middle is hollowed by a gutter or 

 furrow, more or less broad, more or less prolonged in front, 

 but, in general, of a greater extent in the females than in the 

 males. This lower surface of the breast-plate is composed of 

 two orders of pieces : the first, which are medial, and much 

 larger than the others, are called sternal pieces ; the others, 

 being lateral, are termed latero-sternal pieces. Between these 

 pieces and the lateral and inferior edges of the carapace, are 

 situated the feet. 



Among the entomostraca, some, as apus and hranchipes, 

 have the body annulated underneath, as well as above, and 

 have no traces of latero-sternal pieces, while others have no 

 indication of divisions whatsoever. 



The name of tail or abdomen is reserved for the terminal 

 part of the body, which contains only the posterior part of the 

 intestine. The anus is at its inferior face, to which also the 

 branchial feet are sometimes attached. In some Crustacea, it 

 contains the organs of generation ; and in many it is furnished 

 at its extremity with natatory appendages. In the decapod 

 Crustacea, this tail is always folded under the body, and closes 

 the furrow or longitudinal gutter of the sternum. It forms 

 with this furrow a sort of box, in which the eggs are received 

 and lodged at the period of laying. The tail of the males is 

 placed entirely in this furrow. 



The macrourous Crustacea have received this appellation in 

 consequence of the extent of the tail ; it is sometimes soft, 

 and without distinct rings, as in pagurus, sometimes very 

 solid and very muscular. A most remarkable circumstance is, 

 that the paguri betake themselves to the cavities of univalve 

 shells, and that the spiral form of these cavities takes away 



