154 ARTHROPODA. 



pod, a lateral branch, the exopod, and a median branch, the 

 endopod. This branched type of appendage is designated as 

 biramous. What is its use? Compare with this the modified 

 sixth pair of pleopods, called the uropods. 



Make a drawing of one of the fifth pleopods. 



(6) In front of the chelae will be seen the sixth pair of mouth 

 appendages, the third maxillipeds. Remove that of the right 

 side and compare it with the fifth pleopod. In addition to the 

 protopod, exopod, and endopod, it bears a long blade, the epipod t 

 which extended into the gill chamber. The protopod is com- 

 posed of two segments, coxopod and basipod; the endopod of five, 

 segments, ischipod, meropod, carpopod, propod, and dactylopod. 

 The exopod is composed of one long and many short segments. 

 How is the appendage modified to serve in feeding ? 



Make a drawing of the third maxilliped. 



(c) Remove the remaining five mouth appendages and com- 

 pare each with the third maxilliped. These are, beginning pos- 

 teriorly, the second maxilliped, first maxilliped, second maxilla 

 (with a broad paddle, the scaphognathite, the use of which 

 should be understood), first maxilla, and the mandible. Just 

 back of the mandibles are two small flaps, the paragnatha, 

 which are not true appendages. Do you understand the use 

 of each of these appendages? Most of the appendages have 

 parts that may be compared with the typical biramous appen- 

 dage, but they are much modified to serve special functions, and 

 the exact homologies are not important. Between the man- 

 dibles note the mouth, bounded in front by the labrum. 



Drawings of these appendages may be made if time permits. 



(d) The antennae are biramous. Notice on the ventral side of 

 the basal joint of an antenna the opening of the green gland or 

 nephridium. 



(e) The antennules, though branched, are not considered to 

 be of the biramous type. Do you know why ? Remove one and 

 note on the dorsal surface of the basal joint a groove at whose 

 median extremity is a small hole, the opening into the otocyst. 

 Do you know the probable function of the antennules and of 



