Anterior aorta 



THE PHYLA ARTHROPODA AND ONYCHOPHORA 



Heart with ostia 



Posterior 

 Pericardial / Sternal aorta 



cavity / artery 



Lateral 

 cephalic 

 artery Afferent 



branchial Efferent 

 vessel branchial 

 ^ vessel 



Brain 



Ventral 



thoracic 



artery 



Abdominal 

 sinus 



Fig. 15.5. General relationship of the vascular, digestive, and nervous systems of the crayfish; 

 semidias;rammatic. A, vascular system; distributing vessels are shown in black; collecting 

 vessels and sinuses are stippled. B, digestive system (stippled) and nervous system (black); 

 the large digestive glands, which occupv much of the space in the cephalothorax, have been 

 omitted from this diagram. (Modified after K. von Frisch, 1952, Biologic, vol. 1, printed by 

 permission of Baverischer Schulbuch-Verlag.) 



from endoderm during development. The remainder of the digestive tube is 

 lined by tissues derived from ectoderm and is covered by a cuticle of varying 

 thickness. 



The digestive glands, and the viscera generally, are surrounded by extensive 

 cavities through which blood flows after it has left the arteries (see p. 432). 

 These cavities, because they contain blood, are collectively termed the 

 hemocoel. They are not homologous with the coelomic cavities of other 

 schizocoelous forms, although the true coelomic cavities of the embryonic 

 stages may contribute slightly to their formation. More definitely identifiable 

 remnants of the embryonic coelom are found as sacs at the inner ends of the 

 excretory organs, and perhaps as the cavities within the hollow ovaries 

 and testes. 



431 



