AQUATIC INSECTS IX NEW YORK STATE 307 



stems examined were found numerous examples of larvae with 

 their caudal spines pushed into the tissue of the plant clear- 

 up to their bases. In every case noted the larvae were at the 

 apex of vigorously growing stems. As was described above^ 

 the larva eat large round holes in the apices of the growing 

 stems, and this gnawing of the holes is undoubtedly done while 

 the larva is respiring, as I have observed many larvae in the 

 characteristic attitudes shown on plate 28, figure 1, and plate 

 27, figure 18. These figures, I think, show the larvae in a 

 frightened attitude, which resulted from pulling the plant from 

 the mud, and, as a result, one larva stopped feeding while 

 the other stopped respiring. 



Every investigator who has studied the function and struc- 

 ture of the caudal spines has arrived at a different conclusion. 

 Perris, who studied Donacia sagittariae in 1848, was 

 unable to determine the function of the caudal spines and 

 thought there was a delicate membrane, that is the spiracles at 

 the base of the spines, stretched over the opening, and that 

 there was an osmotic interchange of the air of the tracheal sys- 

 tem with that on the exterior of the membrane; but. when 

 we consider the size of the membrane and that there is water, 

 not air, on its exterior surface, this suggestion is seen to be 

 incorrect. Von Siebold, who studied Donacia linearis 

 in 1859, concluded that the openings at the base of the spines 

 were functional spiracles, and that the larva obtained its air 

 supply from the intercellular air spaces of the plant, and this 

 was accomplished by the larva eating a hole into the tissue of 

 the plant, into which it later inserted its caudal spines. From 

 what follows it will be seen that von Siebold came nearest to 

 the correct interpretation of the conditions existing here of 

 any of the investigators. The next investigator to consider 

 this question was Dr E. Schmidt-Schwedt in 1887, who studied 

 the larva of Donacia crassipes. He found that some 

 larvae, kept in a breeding cage, would, when the cage was dark- 

 ened, insert the tips of their caudal spines into the tissue of the 

 roots, but removed them as soon as the cage was lighted again. 



