STRAW-COLOURED GNAT. 



preserve it for the microscope, this change may be retarded by 

 keeping it in clear spring or river water. The former seldom offers 

 sustenance to animalcules, and, therefore, effects this object, which 

 is often very desirable, on account of the scarcity of this species. 



The transformation of this animal from the larva to the pupa is 

 one of the most singular and wonderful changes that can be con- 

 ceived ; and, under the microscope, presents to the admirer of 

 nature a most curious and interesting spectacle. Although the 

 whole operation be under the immediate inspection of the observer, 

 yet so complete is the change, that its former organisation can 

 scarcely be recognised in its new state of existence. 



If we now compare the different parts of the larva with the. 

 pupa, we remark a very striking change in the tail, which, in the 

 previous state of being, was composed of twenty-two beautifully 

 plumed branches, while, in the latter, it is converted into two 

 fine membranous tissues, ramified with numerous vessels. This 

 change appears the more remarkable, as not the slightest resem- 

 blance can be discovered between them, nor are the vestiges of the 

 former tail readily found in the water. The partial disappearance 

 of the shell-like or reniform bodies is another curious circumstance. 

 The lower two, it may be conjectured, go to form the new tail; 

 for, if the number of joints be counted from the head, the new tail 

 will be found appended to that joint which was nearest to them in 

 the larva state, as referred to by the dotted line d, connecting 

 figs. 1 and 2. The two small horns, c c, which form the white- 

 plumed antennae of this species of gnat, when in its perfect state, 

 are discernible in the larva, folded up under the skin near the 

 head at c, in fig. 1. The alimentary canal appears nearly to 

 vanish in the pupa, as in that state there is no necessity for it, 

 the insect then entirely abstaining from food ; while, near this 

 canal, the two intertwined vessels, seen in the larva, have now 

 become more distinct, and are supplied with several anastomosing 

 branches. 



During the latter part of the day on which the drawing (fig. 2) 

 was taken, the rudiments of the legs of the perfect insect might 

 be seen, folded within that part which appears to be the head of 

 the pupa, and several of the globules had vanished, those remaining 

 longest that were situated near the head. It may be necessary to 

 observe, that the head of the pupa fioats just under the surface of 

 the water ; and the insect, in this state, is nearly upright in that 

 fluid, while the larva swims with its body in a horizontal position, 

 or rests on its belly or sides, at the bottom of the pond or vessel 

 in which it is kept, the fringed tail being downwards. 



The colour of the larva when young is a faint and scarcely 

 perceptible yellow ; but as it approaches the change, it assumes a 



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