i 5 2 ELEMENTARY BIOLOGY. [CHAP. 



o. The most anterior ambulatory leg : resembling 

 y. closely and, like it, bearing a gill. 



b. The great chelce: much larger and more powerful 

 than the last appendage: but resembling it in 

 structure, except that its ischio-podite and basi- 

 podite are ankylosed together; it carries a gill. 



c. The three maxillipedes. 



a. The most posterior : its short thick basal two- 

 jointed {protopodite} : the three prolongations 

 articulated to it; the external (epipodite) a 

 curved elongated lamina lying in the branchial 

 chamber and bearing a gill ; the middle one 

 (exopodite) long, slender and many-jointed; 

 the internal one (endopodite) several-jointed 

 and much resembling one of the ambulatory 

 limbs. 



/3. The middle maxillipede : much like a. but 

 with the two joints of the protopodite fused 

 together and with a less stout endopodite. 



7. The anterior maxillipede; protopodite, exopo- 

 dite and epipodite all present, but smaller 

 than those of /3. and the epipodite bearing no 

 gill ; the endopodite flattened and foliaceous. 

 The ambulatory limbs, great chelae, and 

 maxillipedes together constitute the append- 

 ages of the thorax ; we now come to those of 

 the head proper. 



d. The two maxilla. 



a. The posterior: its protopodite and endopodite 

 essentially like those of the anterior maxilli- 

 pede; the epipodite and exopodite united and 



