37S ARTHROrODA 



i;ill chamber being modified into a kind of lung tra\-ersed l\v numerous 

 blood-vessels. In the palm crab (_lig. 300) the gill chamber is di\-ided 

 into two portions, the upper part being pulmonar\-, the lower containing 

 the reduced gills. 



Correlated to this localized respiration is the nearly closed circulatory 

 system [hg. 400, .1, B). The heart (/;), a compact pentagonal organ, 

 receives its blood from the pericardial sinus (pc) through three pairs of 

 ostia, and forces it out through live arteries to the capillary regions of the 

 body. The venous blood collects in a large venous sinus at the base 

 of the gills (f). passes thence through gills, and is returned by several 

 brancliial veins {I'br) to the pericardium. 



pdiM 



plbrt 



Fig. 3qS. — Gills of .4 .t/jr»,t exposed bv cutting away the brancliiosteeiitc. pjh. plh, 

 podo- and pieurobranchia of the corresponding segments; r, rostrum; t. stalked eyes; 

 2, 3. antenna;; 4-6, mandibles and ma.xiUa;; 7-9, ma.xiUipeds; 10, 14. bases of thoracic 

 eet; 15, first pleopod. 



The ahmentary canal is straight and has only one conspicuous enlarge- 

 ment, the so-called stoDiacli (tig. 400, .1, in), divided ii^to two portions, 

 an anterior [cardiac) sac, lined with chitinous folds and teeth and serving 

 to chew the food and bearing in its walls the 'crab-stones,' masses of 

 calcic carbonate stored up to harden the armor rapidly after the molt. 

 The second (pyloric) portion of the stomach is guarded by hairs and 

 serves as a strainer, allowiitg only food sulliciently comminuted to pass. 

 The two liver lobes — voluminous masses of branched glandular tubes 

 (/) open just beliind the stomach. 



The two antennal glands [C. i^d), each provided with a large urinary 

 bladder (M), are dirty green iti color, whence the name green glands often 

 given them. The gonads (fig. 401) lie close beneath the heart, those of 

 the two sides being united liehind, while their ducts remain separate. 

 The structure of the nervous system is in part dependent upoit that of the 

 abdomen. In the Macrura (lig. 400, C) the \entral chain consists of 

 si.x ganglia in the thorax, six in the al>domen, but in the Brachvura 



