"272 W. SAVILLE-KENT, CONTRIBUTIONS TO A 



Claparede in thus demonstrating the true nature of these so- 

 called tracheal stigmata recorded of Atax honzi the existence 

 of certain circular epidermic areas which readily coloured under 

 the action of osmic acid, and which he anticipated might be 

 connected with a respiratory function. Of the allied form 

 Atax ypsilophorus he further reported detecting in rare instances 

 and in young examples only a system of tubular channels con- 

 taining a clear fluid, which, having their origin in the neighbour- 

 hood of the rostrum, were developed backwards into various 

 branches along the dorsal surface and opened apparently with 

 infundibulate expansions upon the perivisceral cavity. The 

 respiratory apparatus of the adult animals as represented by 

 distinct air-passages or tracheae appears to have altogether escaped 

 Claparede's observation, possibly from his investigations having 

 been conducted in connection with alcoholic specimens, under 

 which conditions the tracheal tracts become more or less com- 

 pletely obliterated. 



Dr. P. Kramer, as the result of a much more recent examina- 

 tion of this group,* has declared that the tracheal passages of 

 the Hydrachnidae, coalescing so as to form two single tubular 

 passages in the neighbourhood of the head, finally open externally, 

 as in the Tromfidiidae, by two distinct though closely approxi- 

 mating apertures upon the summit of the rostrum. In this 

 manner they are held to differ more especially from the Oribati- 

 dae, Gamasidae and Ixodidae, in which the tracheal stigmata 

 open respectively upon the thorax or a yet more posterior 

 region of the ventral surface. Dr. S. Haller f has still more 

 recently endorsed Kramer's declaration with respect to the 

 tracheal openings of the Hydrachnidae, but, as I now propose 

 to demonstrate, the interpretation arrived at by these two 

 authorities is incorrect to the extent that they have altogether 

 overlooked a not easily recognised but at the same time very 

 important structural point. The opening of the tracheal 

 tubuli directly upon the external surface after the manner of 

 ordinary terrestrial air-breathing arthropods, as maintained 

 by Kramer and Haller, has, T must confess, appeared to me 



* " Zur Naturgeschichte der Hydrachniden " and " Grundziige zur 

 Systematik der Milben," Troschel's Archivfilr Naturgesch. 1875, 1877. 



f " Die Hydrachniden der Schweiz," Mitth. Bern, naturforschende Gesell- 

 -schaft, 1882. 



