138 



RESPIRATORY MECHANISMS 



In special experiments it was shown that the compressibility 

 of the tracheal system, including the air sacs, is so slight that 

 an efficient ventilation is not within the power of the animal, 

 and the air sacs can function, in so far as they have any 

 respiratory significance, only as an oxygen store. 



Fig. 80. Donatio, larvae and pupae on Ranunculus roots (see text). About natural 



size. (Boving.) 



While the respiratory mechanism of the Mansonia larva ap- 

 pears simple and reasonably clear, the same cannot be said of 

 the Donacia larvae. These animals, shown in Fig. 80 on the 

 roots of Ranunculus from which they feed, possess in connec- 

 tion with each of the last abdominal spiracles a slightly bent 

 very sharp chitin thorn (89 cy) which is inserted into the root 

 (86 bq). 



