508 



ZOOLOGY 



SECT. 



channels and containing gland-cells, which will be referred to 

 presently. 



According to their point of origin, the gills are divisible into 

 three sets first, podobranchice or foot-gills, springing from the 

 epipodites of the thoracic appendages, from which they are only 



Fie;. 4(iL'. Kespir.-itnry organs of Astacus fluviatilis. In A the gill-cover is removed and 

 the- gills undisturbed; in B the podobranchise are removed and the outer arthrobranchia- 

 turned d<i\vn. KJ., antunnule ; <(.,., antenna; o'jj., first ; 062-, second abdominal segment ; 

 </./'. 7 IS, inner arthrobranchise ; arb'. , 12, outer arthrobranchias ; ep. 5, scaphognathite ; 



jill>. 11 13, ploiirobraiu-hiii' ; //'.. ; -?..'. pudnliraiifhs ; jil. 1, first pleopod ; 6 13, thoracic 

 appendages. (From Lang's Coii<j>n,-<tti,;. Anatomy, after Huxley.) 



partially separable; secondly, arthrobranchice or joint-gills, spring- 

 ing from the articular membranes connecting the thoracic 

 appendages with the trunk ; and thirdly, pleurobranchice, or wall- 

 gills, springing from the lateral walls of the thorax, above the 

 attachment of the appendages. It is inferred from the study of 

 other Crayfishes, that a typical thoracic segment bears four gills, 

 podo-, two arthro-, and one pleurobranchia. But in Potamobia 



