274 W. SAYILLE-KEKT, CONTRIBUTIONS TO A 



iincl, not only a moditication of the respiratory apparatus hitherto- 

 not known to obtain in any representatives of the Arachnicla^. 

 but a condition which as developed here in the adult state cor- 

 responds with what is met with only during the larval condition 

 in the class Insecta. These cephalic tracheo-branchiae as de- 

 veloped in Limnesia histrlonica have been identified in Uydrachna 

 iflohula, where the membranovTS tracheal sacculi project in a more- 

 horizontal direction from the roof of the rostrum, and also in 

 Diplodontus fiUjjes, A tax honzi, Atax crassijjes^ and indeed in all 

 the species specially examined for these structures. Examined 

 without dissection either living or dead it has been found im- 

 possible to recognise the existence of these tracheal-gills, they 

 being under such circumstances concealed and at the same time 

 effectually protected by the overhanging convexity of the anterior 

 region of the animal's body ; while in order to display it in 

 connection with its basis of attachment, the greatest care is 

 requisite to avoid lacerating in the operation of severing the 

 rostrum from the body the delicate membrane of which it is 

 composed. 



According to Kramer's representation, that portion of the 

 tracheal system which ascends vertically to the roof of the rostrum 

 consists at least in the unnamed species of yesaea which he 

 iigures of two corresponding relatively large tubuli that- 

 exhibit, as in the trachea of the Insecta, a distinct spiral 

 librillation, out of which at their lower or proximal end directly 

 decussate a number of the simple unstriated tubuli as dis- 

 tributed throughout the body. In no instance up to the present 

 time have I been able to corroborate Kramer in this particular,, 

 in all examples personally examined the tracheal tubuli produced 

 from the sides of the oesophagus to the summit of the rostrum, 

 though so closely approximated as seemingly at hrst sight to 

 form a single tube, remaining distinctly separate throughout 

 their course and forming independent terminations within the gill- 

 like membranous expansion just described. No spiral librillation 

 could in any case be detected, and in this circumstance the 

 tracheae agree with what obtains in all known representatives of 

 the Arachnida class. The tracheal tubuli of the Hydrachnidae, 

 it is worthy of note, with regard to the absence of a spiral 

 filament, their generally unbranched character and paniculate 

 disposition, accord in a remarkable manner with the same struc- 



