TRACHEATA. 



409 



observations (Kraepelin, etc.), and if it holds true for the Bee must be regarded 

 as correct for other cases also. 



As to the order of the appearance of the appendages observations are as 

 yet too scanty to form any complete scheme. In many cases all the appen- 

 dages appear approximately at the same moment, e.g. Hydrophilus, but 

 whether this holds good for all Coleoptera is by no means certain. In Apis 

 the appendages are stated by Biitschli to arise simultaneously, but according 

 to Kowalevsky the two mouth appendages first appear, then the antennae, 

 and still later the thoracic appendages. In the Diptera the mouth appen- 

 dages are first formed, and either simultaneously with these, or slightly later, 

 the antennae. In the Hemiptera and Libellulidae the thoracic appendages 

 are the first to be formed, and the second pair of maxillae makes its appear- 

 ance before the other cephalic appendages. 



The history of the changes in the embryonic appendages during the 

 attainment of the 'adult con- . 



dition is beyond the scope 

 of this treatise, but it may 

 be noted that the second 

 pair of maxillae are rela- 

 tively very large in the 

 embryo, and not infre- 

 quently (Libellula, etc.) 

 have more resemblance to 

 the ambulatory than to the 

 masticatory appendages. 



The exact nature of the 

 wings and their relation to 

 the other segments is still 

 very obscure. They ap- 

 pear as dorsal leaf-like ap- 

 pendages on the 2nd and 

 3rd thoracic segments, and 

 are in many respects simi- 

 lar to the tracheal gills 

 of the larvae of Epheme- 

 ridae and Phryganidae (fig. 

 1 88 A), of which they are 

 supposed by Gegenbaur 

 and Lubbock to be modifi- 

 cations. The undoubtedly 

 secondary character of the 

 closed tracheal system of 

 larvae with tracheal gills 

 tells against this view. 

 Fritz Miiller finds in the 

 larvae of Calotermes ru- 



FIG. 188. FIGURES ILLUSTRATING AQUATIC RE- 

 SPIRATION IN INSECTS. (After Gegenbaur.) 



A. Hinder portion of the body of Ephemera 

 vulgata. a. longitudinal tracheal trunks; b. alimen- 

 tary canal ; c. tracheal gills. 



B. Larva of ^Eschna grandis. a. superior longi- 

 tudinal tracheal trunks ; b. their anterior end ; c. por- 

 tion branching on proctodaeum ; o. eyes. 



C. Alimentary canal of the same larva from the 

 side, a, b, and c. as in B ; d. inferior tracheal trunk ; 

 e. transverse branches between upper and lower 

 tracheal trunks. 



