SEA-FISHERIES LABORATORY. 341 



covering the chitinous in tegument. So that wherever a 

 seta arises the continuity of the thick exoskeleton is 

 broken in order to allow this tube-like prolongation to 

 reach the exterior. The contents of the setae are proto- 

 plasmic and are connected with the epidermis. In some 

 regions of the body the. setae have nerve fibres passing to 

 their interior. These are the sensory setae, of which there 

 are several kinds (see section on Sense Organs). The setae 

 may be simple prolongations, or they may consist of a 

 central axis, from which arise off-shoots. In the latter 

 case the cavity of the central axis is not continued into 

 the lateral out-growths. In addition to the setae 

 described above, there are small papillae on the surface 

 of the shell, which are merely thickenings of the cuticle 

 and do not contain a cavity. Yitzou states that in 

 Portunus these cuticular processes are comparatively 

 long. In Cancer, however, they are extremely small, and 

 can only be detected under the microscope. Yitzou 

 affirms that the long " setae,'' present in the w x alls of the 

 fore-gut, have no central cavity, and are probably merely 

 extremely large cuticular prolongations and not true setae. 

 These " setae " in the fore-gut act as strainers. Where 

 the sub-branchial region of the carapace is closely applied 

 to the bases of the thoracic legs there is a rich growth of 

 setae. These probably assist in preventing the water 

 from entering the branchial chamber at the base of the 

 thoracic legs. 



The inhalent branchial opening is also well guarded 

 by long setae, both on the flabellum of the third maxilli- 

 pede and on the anterior border of the coxopodite of the 

 chela. The setae on the endopodites of the pleopods in 

 the female are used for the attachment of the egg*. 



