THE CANADIAN ENTOMOLOGIST. 253 



them by osmosis, a highly improbable conjecture, considering the small 

 surface they allow for such diffusion. Von Seibold (Amtlichen Bericht 

 der 34sten Versalung der deutschen Naturforschen und Aerste, 

 Karlsruhe, 1859, Seite 211), in describing D. linearis, thinks these to be 

 true stigmata and that the larvge breathe the air found in the intercellular 

 spaces of the roots, first eating into the root and then inserting the sickle- 

 shaped appendages so that the stigmata are placed close to the openings 

 thus made. 



The most careful study of this matter has been made by Dr. E. 

 Schmidt-Schwedt (Bui. Ent. Zeit., Bd. XXXI., Heft II., p. 325, PI. V., 

 figs, i-ii, 1887) upon Donacia crassipes, Fab. The cocoons were found 

 in October on the roots of the white water lily [Nymphea alba), and were 

 usually found to contain beetles. How these were filled and kept 

 replenished with air was a problem which had never been satisfactorily 

 explained. He soon found an opening toward the end of the cocoon on 

 the side next the root leading into a passage communicating with the air 

 passage in the root, which explained how the cocoon might readily 

 become filled with air coming out from the root and expelling the water. 

 Though not entirely clear, I should judge from the figures and text that 

 he believed this air passage to be a cavity eaten out by the larva. Later, 

 however, he describes and figures the cavities made through the cocoon 

 and into the root tissues by the two appendages. In the cocoons of 

 D. piscatrix and Hamonia nigricornis it is clear that the cocoon is entire 

 next to the root, with the exception of a pair of elliptical holes at one end, 

 leading to two corresponding cavities in the roots and very evidently 

 formed by these appendages. I could find no marks of feeding beneath 

 the other ends of the cocoons, and at least the air is replenished if it is 

 not originally taken into the cocoon through these two passages. Dr. 

 Schmidt-Schwedt points out that usually when a plant is thus wounded a 

 corky formation ensues, but that such is not the case in this until the 

 beetle has emerged from the cocoon and the water is admitted, when a 

 cork formation at once takes place and the passage is closed. It seems 

 evident that the larva, breathing as will be further described, merely 

 forms the cocoon close to its body, thus expelling all the air, withdraws 

 the appendages from the two passages and transforms to the pupa, which 

 thus admits the air from the roots and remains open, replenishing the air 

 for the pupa and beetle. 



Concerning the structure and function of these larval appendages, he 



