BIOLOGY AND STRUCTURE OF HYDROPHILUS CARABOIDES 649 



taenidia is disputed by E. Schneider (1902), who writes on 

 the tracheae of H y d r o p h i 1 u s p i c e u s as follows : ' . . . eine 

 faserartige Verdickung der Intima existiert aber nicht, es kann 

 also nur von einer Hpiralfalte geredet werden. Genaue Unter- 

 suchung zeigt folgendes. Zu unterscheiden sind die Furchen, 

 welche eine Falte begleiten, ferner die steil aufsteigenden 

 Faltenwiinde und die flache Faltendecke, deren Breite im 

 Durchschnitt der einer Fiirche entspricht. An geschwarztem 

 Materiale treten entweder die Wande als schwarze Striche, die 

 parallel nebeneinander verlaufen, oder die Faltendecken als 

 schwarze Streifen scharf hervor, wahrend die Furchen innner 

 massig dunkel erscheinen ' (loc. cit., p. 505). 



When stained with iron haematoxylin, or Giemsa's stain, the 

 taenidia of the main tracheal trunks of the larva of H , c a r a - 

 boides stand out vividly on the colourless ground of the 

 chitinous cuticula, from which they are more separated, than 

 the structures in the shape of grooves or folds. 



In the taenidia just described I succeeded in observing 

 character of their structure which bears evidence in favour 

 of their strong individualization from the lining of the tracheae, 

 of which the former are of course a product. Thanks to the 

 comparatively considerable thickness of the taenidia, their 

 heterogeneous structure is plainly visible in sections (transverse, 

 or better in tangential sections). The taenidium is a thin- 

 walled capillary tube, as the darker wall and the lighter lumen 

 are easily distinguished. 



This structure has a certain meaning. The walls of the 

 tracheae must possess a considerable elasticity, as for breathing 

 purposes their lumen must be open for the passage of air. 

 Besides, they perform another function of a more mechanical 

 significance, i. e. they are the ligaments that hold the organs 

 in their mutual position. Finally, the tracheae represent 

 elastic pillows, which lie between different internal organs. 



The latter function of the breathing tubes is clearly visible 

 in the larva of H . c a r a b o i d e s , since the greater half of the 

 cross-section of the abdomen is occupied by the tracheae. 

 Between the latter passes the hind intestine, which, when over- 

 filled with excrements, presses on the adjacent walls of the 



