206 



COLLEGE ZOOLOGY 



DESCRIPTIVE TABLE OF THE HOMOLOGOUS 



(Continued) 



APPENDAGES OF THE CRAYFISH * 



SEGMENT 

 NUMBER AND 



NAME 

 OF APPENDAGE 



PROTOPODITE 



EXOPODITE 



ENDOPODITE 



FUNCTION 



* The antennules are not included in this table because they are considered by Snodgrass and other au- 

 thorities as prostomial sense organs, as are the eyes. 



which not only form the digestive enzymes 

 but also absorb some of the products of 

 digestion. Undigested particles pass on into 

 the posterior end of the intestine, where 

 they are gathered together into feces and 

 pass through the anus. 



Circulatory system 



Blood. The blood plasma, into which the 

 absorbed food passes, is an almost colorless 

 liquid, but contains hemocyanin, a bluish 

 respiratory pigment that contains copper in- 

 stead of iron. There are suspended in the 

 plasma a number of amoeboid cells, the 

 blood corpuscles. The principal functions 

 of the blood are transportation: it transports 

 food materials from one part of the body 

 to another, oxygen from the gills to the 

 various tissues, carbon dioxide to the gills, 

 and waste products to the excretory organs. 



If a crayfish is wounded, the blood thickens, 

 forming a clot; it is said to coagulate. This 

 clogs the opening and prevents loss of 

 blood. 



Blood vessels. The principal blood vessels 

 (Figs. 114 and 116) are a heart, 7 main 

 arteries, and a number of spaces called 

 sinuses. 



Heart. The heart is a muscular-walled, 

 saddle-shaped sac lying in the pericardial 

 sinus in the median dorsal part of the thorax. 

 It may be considered a dilatation of a dorsal 

 vessel, resembling that of the earthworm. 

 Blood enters the heart through three pairs 

 of valves called ostia, one dorsal, one lateral, 

 and one ventral. 



Arteries. Five arteries arise from the an- 

 terior end of the heart. 



1. The ophthalmic artery is a median 

 dorsal tube passing fonvard over the stomach 



