80 



a pair of dorsal extensors, and a pair of ventral flexor 

 muscles. 



Somite I. Each extensor (ex. 1) arises as a broad band 

 of muscle from the top of the epimeral region of the last 

 two thoracic somites. It passes inward and backward, 

 and is inserted on the side of the anterior triangular 

 portion of the tergum of the first somite. 



Each flexor (/. 1) muscle arises from the " sella 

 turcica " in the thorax, and passes backward near the 

 median line. It is inserted on a small ingrowth of the 

 sternum immediately in front of the arthrodial membrane 

 separating the first sternum from the second. 



Somite II. Each extensor (ex. 2) is inserted on a 

 small concavity in the tergal region of the first somite. 

 It passes backward, and is inserted near the middle line 

 on a tendon which is attached to the anterior extremity of 

 the second somite. 



Each flexor (f. 2) arises from the posterior face of the 

 ingrowth, or tendon, at the posterior end of the first 

 sternum. It passes backward near the median line, and 

 is inserted on the anterior face of a similar tendon at the 

 posterior extremity of the second sternum. 



Somite III.-YI. and Telson. The muscles in the 

 succeeding abdominal somites have the same arrange- 

 ment as those of the second somite. The flexor of the last 

 abdominal somite is not inserted on a well-marked tendon. 

 The same applies to both the origin and insertion of the 

 flexor muscle of the telson. 



Uropod of female (PI. IV, fig. 25). 



In their natural position the uropods are extended 

 and lie almost horizontal, with their distal extremities 

 pointing toward the posterior end of the abdomen. 



The Protopodite is capable of two kinds of move- 

 ment. First there is a movement in an antero-posterior 



