148 



THE CRAYFISH 



of the intestine, and the digestive glands. Lift the heart carefully and 

 observe the single sternal artery (descendant artery) passing ven- 

 trally. It can be seen to connect with the subneural artery which 

 carries blood both anteriorly and posteriorly in the ventral region. 

 Determine if possible exactly what structures are supplied by the 

 branches of the subneural artery. From all these arteries blood 

 escapes into intercellular spaces from which it flows back into an 

 unpaired ventral sinus (sternal sinus). In the thoracic region this is 

 joined to paired lateral sinuses by five pairs of small canals. From 

 these lateral sinuses afferent branchial vessels carry blood to the 

 gills; efferent branchial vessels return blood from the gills by way 



anterior aorta /a6ero/ cep/iaZ/c orterij 

 antennu/e Xstomctic/? \ heart 05tfa 



pericard/af 

 £>i'nua 



antenna 



grreen^ 

 ^/anaf 



rior aorta 



ventral abcfom/'na/ 

 arterij 



'ntc5t/n& 

 ^nus 



e£>opha^U5 



y/5cerat 

 artera 



Fig. 66. — The digestive and arterial systems of the crayfish; arrows indicate 

 the direction of blood flow (c/. Fig. 65). 



(Redrawn with modifications from G. B. Howes, "Atlas of Zootomy, 

 by Macmillan and Co., Ltd., printed by permission.) 



copyright, 1902, 



of six pairs of branchio-pericardial canals to the pericardial sinus (c/. 

 Fig. 65). It is impracticable to dissect out parts of the circulatory 

 system other than the arterial portions. Add the observed portions of 

 the circulatory system to your previous figure. 



(d) Remove the heart and look for ostia on its ventral surface. 

 Note the Y-shape of the reproductive organs, and find their ducts 

 leading to the external openings previously noted. Remove the repro- 

 ductive organs, being careful not to injure the digestive glands or the 

 intestine. Trim off more of the gills and pull away the portions of 

 the abdominal extensors that remain in the thorax. Make out the 

 connection of the gastric mill with the intestine and the antero- 

 posterior extent of the digestive glands. Cut in from one side and 

 find the esophagus. It is very short and can be best located by noting 

 again the position of the mouth. Trace the intestine to its posterior 

 end, cut off close to the anus, and carefully free it up to its union with 

 the stomach ; also free the digestive glands. Cut across the esophagus, 

 and remove the entire digestive tract and its appended glands in one 



