

ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



(Malpighian tubes) opening into the alimentary canal 

 be front limit of the proctodaeum. 



In connexion with the disappearance of the nephridial tubes during 

 the evolution of the Arthropoda it should be remembered that in this 

 phylum the function of excretion is carried out to a great extent by the 

 skin, waste nitrogen being contained in the chitin which covers the 



Light 



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V 



\, 



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r \ 



.-.- \ 



T 



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FIG. 105. 



I ;il.mt coo homopterous insects which alighted on a sheet of paper and 

 a lamp. 



IHoD of the I'.MK axes of the insects' bodies : the two fine lines 

 OUtOC of li.^ht. 



ml is -,t rid of at each ecdysis. Furthermore the coloured 



'i' h are often present in the exoskeleton are excretory sub- 



for example, in the group to which our common Cabbage 



' belong the characteristic white pigment is impure 



1. while the orange and yellow pigments are derivatives of uric 



H" 1 Arthropod then has developed the habit of depositing its 



'<<"> material in insoluble form on the surface of its 



