248 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH, 
extent than those do from one another. The gills are, 
in fact, reduced to seventeen on each side, in consequence 
Fig. 68. Cambarus Clarhii, male (4 nat. size), after Hagen. 
of the absence of the pleuro-branchia of the last thoracic 
somite; and there are some other differences to which 
it is not needful to refer at present. It is convenient to 
