240 



RESPIRATORY APPARATUS OF CRUSTACEA. 



b ve 



number of pyramids, each composed either of a number of 

 minute cylinders placed like the hairs of a brush, or of little 



lamellae piled one on 

 the other like the 

 leaves of a book. 

 These organs are fixed 

 by their extremities 

 to the inferior border 

 of the arch of the 

 flanks (Fig. 574) ; 

 and are inclosed in 

 two large cavities, 

 situated at the side of 

 the thorax and shut in 

 between the carapace 

 and the arch just men- 

 tioned, an arrangement which is not found in the other divisions of 

 this class. The respiratory cavity communicates with the exterior 



FJO. 574-. VERTICAL SECTION OF A CRUSTACEAN, SHOW- 

 ING THK COURSE OF THE BLOOD ; c, heart ; *, venous 

 sinus ; va, vessels conducting the venous blood to the 

 gills ; ve, vessels which collect the aerated blood from 

 the capillaries of the gills ; vb, branchiocardiac vessels ; 

 /, carapace ; st, sternum. 



FIG. 575. RESPIRATORY APPARATUS OF PRAWN ; a, rostrum or beak ; 6, carapace ; c, 

 base of antennae ; d, base of abdomen ; e, base of legs ; /, gills ; g, dotted line, marking 

 the turned-in border of the portion of the carapace that covers in the gills, which has 

 been removed in this preparation ; h, canal for the exit of the water from the respira- 

 tory chamber ; {, its valve ; j, its extremity. 



by two openings ; that which serves for the entrance of the 

 water is situated between the base of the legs and the side of 



