227 



=3' 



X PHYLUM ARTHROPODA 



stantly moving in one direction, viz., 

 from the heart by the arteries to the 

 various organs of the body, where it 

 receives carbonic acid and other waste 

 matters; thence by sinuses into the 

 great sternal sinus ; from the sternal 

 sinus by afferent branchial veins to the 

 gills, where it exchanges carbonic acid 

 for oxygen ; from the gills by efferent 

 branchial veins to the branchiocardiac 

 veins, thence into the pericardial sinus, 

 and so to the heart once more. 



The nervous system (Fig. 129) con- 

 sists of a brain (g) and a ventral nerve- 

 cord, united by oesophageal connectives 

 (se). The ventral cord is double, but the 

 right and left halves have undergone 

 partial fusion, so that the ganglia, and 

 in the abdomen the connectives also, 

 appear single instead of double. The 

 ventral cord contains twelve of these 

 ganglia, the first is infra-cesophageal, 

 being larger than the others and formed 

 by the union of the ' ganglia belonging 

 to the last three cephalic and first three ' j v 



thoracic segments. All the remaining * 



segments have their own ganglia, with Fig. 129.— Nervous system 

 , . r , , , . , . of Astacus fluviatilis. 



the exception Of the telSOn, Which IS Sup- bg, sub-oesophageal gang- 

 lion ; cs, commissural 

 ganglion; g, brain; s, 

 visceral nerve; sc, oe- 

 sophageal connective; y, 

 post-cesophageal commis- 

 sure ;_ IV- VII I, thoracic 

 ganglia; i-b, abdominal 

 ganglia. (From Lang's 

 Comparative Anatomy, 

 after Vogt and Yung.) 



plied from the ganglion of the preced- 

 ing segment. There is a visceral system 

 of nerves (s) supplying the stomach, 

 originating in part from the brain and in 

 part from the- oesophageal connectives. 



