/. CRUSTACEA: DEC APOD A. 



433 



Correlated to this localized respiration is the nearly closed cir- 

 culatory system (figs. 439, A, B). The heart (/*), a compact 

 pentagonal organ, receives its blood from the uericardial sinus 

 (pc) through three pairs of ostia, and forces it out through five 

 arteries to the capillary regions of the body. The venous blood 

 collects in a large venous sinus at the base of the gills (v), passes 

 thence through gills, and is returned by several branchial veins 

 (vbr) to the pericardium. 



The alimentary canal is straight and has only one conspicuous 

 enlargement, the so-called stomach (fig. 439, A 9 m), divided into 

 two portions, an anterior sac (cardiac pouch), lined with chitinous 

 folds and teeth and serving to chew the food and bearing in its 

 walls the so-called ' crab-stones/ which are masses of calcic carbon- 

 ate stored up to harden the armor rapidly after the molt. The 

 second or pyloric portion of the stomach is guarded by hairs and 

 serves as a strainer, allowing only food sufficiently comminuted 

 to pass. The two liver lobes voluminous masses of branched 

 glandular tubes (I) open just behind the 

 stomach. 



The two antennal glands (fig. 439, C, 

 gel), each provided with a large urinary 

 ^bladder ( bl), are dirty green in color, whence 

 the name green glands often applied to 

 them. The gonads (figs. 440) lie close 

 beneath the heart, those of the two sides 



FIG. 440. FIG. 441. 



FIG. 440. Reproductive organs of (A) female and (B) male crayfish. (From Hux- 

 ley.) od, oviduct; od', its opening on llth appendage; ou, ovary; f, testes; vd, 

 vas deferens ; vd', its opening on 13th appendage 



FIG. 441. Nervous system of crab, Carcinus. (From Gegenbaur.) a, antennal nerves ; 

 c, cesophageal commissures; gi, fused ventral chain perforated for sternal 

 artery ; gs, brain ; o, optic nerve. 



