Observations on the Oribatidse. By A. D. Michael. 19 



possibly arise from oral stigmata, assume greater importance and 

 become some of the largest; a sbort wide trunk leads into a 

 chamber, from which proceed two ceecal prolongations of unequal 

 length (plate I. fig. 7) ; these share with the other tracheae the 

 characteristic of being short, and of the structure described 

 above. 



It is very interesting to find this slightly developed and almost 

 rudimentary condition of the tracheae in the genus Nothrus, when 

 we remember that the nymphs and larvae all through the family 

 usually have the tracheae in a rudimentary state, and that in this 

 genus the want of hard chitinization in the integument of the 

 adults, their great resemblance to the nymphs, their carrying the 

 cast skins in some species, and other indications, seem to point to 

 creatures where the adult shows less progress from the nymphal 

 stage than in other genera. 



In the genus Hoplophora I have hitherto failed to discover any 

 tracheae whatever; Claparede was greatly surprised at the same 

 thing,* he found, beneath Nicolet's stigma, which he calls peritrema, 

 three very minute sacs filled with air, which he says are not longer 

 than the width of the stigma, and which, from his drawing, cannot 

 be above the 1-25 Uth of a millimetre in length (his entire creature 

 being over a millimetre) ; he considers these to be the entire 

 respiratory arrangement of the creature, and to be modified trachea, 

 equivalent to the so-caUed lungs of spiders, scorpions, &c. Although 

 he did not find any leaf-like arrangement within the sacs, or any 

 blood-vascular vessels in connection with them, it must, however, 

 be remembered that Claparede was doubtless relying upon the 

 statement of Nicolet, whose book he quotes, that the tracheae in 

 other species arose from this so-called stigma. 



Claparede expresses his astonishment at the extremely rudi- 

 mentary condition of these respiratory organs, and he well might 

 do so ; one naturally is diffident of questioning a conclusion on this 

 subject arrived at by a man so extremely well acquainted with 

 spiders' lungs as Claparede, but I cannot think that a sufficient 

 respiratory system is shown here ; it seems to me far more likely 

 that these minute sacs are connected with the functions of hearing 

 or smell performed by these pseudo-stigmata as suggested by me in 

 an earlier number of this Journal, and it seems to me that there 

 are other means to be found by which aeration could take place in 

 Hoplophora. We know that in many soft-skinned acari, as Tyro- 

 glyphus, Sar copies, Dermaleichus, &c., respiration is performed by 

 the general body-surface without special organs ; now mSoplophora, 

 in consequence of the movable ventral plate, so different to that of 

 other Orihatidw, its opening and closing must have a bellows-like 

 action, and great quantities of air must be drawn inside the carapace 

 * " Stadien an Acariden," Zeitsclir. f. Wiss. Zool., 1868, p. 512. 



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