432 



NEUROPTERA 



it is usually spoken of as a nymph, but the term larva is also 

 frequently applied to it. Soon the gills begin to appear in the 

 form of small tubular caeca placed in the posterior and upper 

 angles of the abdominal rings ; in fifteen days the gills begin to 

 assume their characteristic form, are penetrated by tracheae, and 



FIG. 276. Nymph of Cloeon dipterum.' 1 Wing-sheath 

 of left side, gills of right side, removed ; g, 

 tracheal gills. (After Vayssiere.) 



FIG. 277. Larvule of Cloeon 

 dimidiatum. (After Lub- 

 bock.) 



the circulation can be seen. The amount of growth accomplished 

 after hatching between March and September is but small. 



The metamorphosis of Cloeon has been described by Sir John 

 Lubbock ; he informs us that the young creature undergoes a 

 constant and progressive development, going through a series of 

 more than twenty moults, each accompanied by a slight change 

 of form or structure. His observations were made on captured 



1 In reference to a doubt as to the name of this nymph, cf. Eaton, Tr. Linn. 

 Soc. Zool. (2) iii. p. 20. 



