54 MICROSCOPIC ILLUSTRATIONS. 



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 conceived; and, under the microscope, pre- 

 sents to the admirer of nature a most curious and inte- 

 resting spectacle. Although the whole operation be 

 under the immediate inspection of the observer, yet so 

 complete is the change, that its former organization can 

 scarcely be recognized 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 resemblance can 

 be discovered between them, nor are the vestiges of the 

 former tail readily found in the water. The partial dis- 

 appearance of the shell-like orreniform bodies is another 

 curious circumstance. The lower two, it may be con- 

 jectured, 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, 



