138 LEAVES FROM MY NOTE-BOOK. 



close observation shows a contrivance of an astonishing nature for 

 obtaining air for respiration. Under a magnifying glass, two 

 slender curved spines may be seen projecting from the hinder end 

 of the dorsal surface, and to the bases of these pass the longitu- 

 dinal air-tubes, which traverse the whole length of the body. At 

 the roots of the spines are a pair of small openings which look 

 likejspiracles. Roots of Nymphcea examined by Schmidt-Schwedt 

 were observed to exhibit peculiar scars ; these were discovered 

 with difficulty, owing to the dark colour and uneven surface of the 

 roots. There was in each case a rough hole, made apparently by 

 the jaws of the larva when feeding, and at a distance corresponding 

 with the le?igth of the body, a pair of small slits. These slits were 

 found to penetrate the epidermis of the roots, and to lead to the 

 small irregular air-spaces, which occupy a considerable part of the 

 interior of the roots. Schmidt-Schwedt believes that these slits 

 are made by the spines, and that the air is drawn in by internal 

 channels running along them. Perhaps no contrivance of aquatic 

 insects for procuring air is so remarkable as this tapping of the 

 reservoirs of air of submerged roots. 



In the pupal stage a fresh arrangement for respiration has to 

 be made. The pupal cocoon is a close-woven, oval capsule 

 attached to the same roots as those on which the larvae feed. On 

 the attached side the wall of the cocoon is deficient, and a good- 

 sized hole, previously closed by the root itself, appears when the 

 cocoon is torn away. A number of small holes, penetrating into 

 the substance of the root, appear upon the plant when the cocoon 

 is detached, and it is probably from this source that the pupa 

 derives its supply of air. Wounds in the living tissue are as a 

 rule quickly repaired by a corky growth, but this is not the case 

 with the hole bored by Donacia larvae in the roots of the water- 

 lily. They remain open so long as the cocoon remains attached, 

 and only become closed by cork, when the cocoon is torn open 

 by the emerging beetle, which has remained all the winter in its 

 pupal cocoon. 



The surface film plays an important part in the peculiar feed- 

 ing and breathing arrangements of the larva of the gnat {Culex). 

 This larva, when at rest, floats on the surface of the water; but 

 whilst feeding — as it does voraciously — it hangs head downwards, 



