82 



M a I 6 a 1» d in <' n • 



There are no extensors between the third and fourth 

 somites, and also between the fourth and fifth somites. 



According to Williamson, there are only two Long 

 flexors a1 each side arising from the thorax. One is 

 inserted on the sternum of the united third, fourth and 

 fifth somites, and the other is inserted on the telson. 



Uropods of Male. These muscles have been described 

 by Williamson.* In the ftrsl appendage llie endopodite 

 has n strong flexor muscle. The extensor is extremely 

 small, and probably the flexion is effected by the elasticity 

 of the arthrodial membrane. The protopodite lias two 



small muscles, one of which Ilexes and the other rotates 



the Limb. In the second appendage there is also ;i strong 

 flexor in the endopodite. I he protopodite has a system of 

 small muscles which rotate, extend and Ilex the appendage. 



Eistology of Muscle. 



The in use I es of Cancer ;i re coin posed of striated fibres. 



Each fibre is an elongated multi-nuclear cell which 

 reveals, in Longitudinal sections ;ind in stained prepara- 

 tions, two kinds of striations Longitudinal and transverse. 

 As a rule, the cross striations are the more obvious, and 



produce the "striped" appearance so characteristic of 

 A rl hropod m usele fibres. 



Each fibre is composed of numerous Longitudinal 

 fibrils, which give rise to the Longitudinal striations. In n 



transverse section across a fibre it is seen thai the filu'ils 



have an unequal distribution, and arc usually grouped 



together into polyhedral areas (Cohnheim's areas). The 

 bundle of fibrils constituting a single area is known as a 

 muscle column. The various muscle columns are separated 



Williamson, II. ('. Twenty-second Annual Report of the 

 Fishery Board for Scotland, p. lot. 



