/. CRU8TACRA: DEC APOD A. 



Correlated to this localized respiration is the nearly closed cir- 

 culatory system (figs. 430, A, B). The heart (It), a compact 

 pentagonal organ, receives its blood from the pericardial sinus 

 (|)(") 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. 430, A, m), divided into 

 two portions, an anterior sac (cardiac pouch), lined v?ith cliitinous 

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

 walls the so-called ' cra,b-stones,' which are masses of calcic carbon- 

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

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

 serves as a strainer, allowing only food sufficiently commiimted 

 to pjass. The two liver lobes — voluminous masses of branched 

 glandular tubes (l) open just behind the 

 stomach. 



The two anteimal glands (fig. 430, C, 

 gd), each provided with a large urinary 

 _4 bladder {hi), 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. «0. Fig. 441. 



V\o. UO. — Heiirodiictive nrgans of (A) fomale and {B) niale crayfish. (From Hux- 

 ley.) of/, oviduct; od\ its opening' on lltli appendage; oi\ ovary; t^ testes: vd, 

 vas deferens ; vd\ its opening on IJJtli appendage. 



Fig. 441.— Nervous system of crali, Carcinns. (From (iegenbaur.) a, antennal nerves ; 

 (', ci?Rox)hageal commissures ; rif\ fused ventral chain perforated for sternal 

 artery ; f/.s', brain ; o, optic nerve. 



