INTERNAL ANATOMY. 93 



tion. He says that he has watched them in action and 

 is convinced of the function. 



Haller,* writing of the Hydrachnidse, although he 

 calls the organs " Haftnapfe," puts that word between 

 inverted commas as if he did not wish to be responsible 

 for it, and expresses an opinion that the organs are too 

 highly organised for suckers and seem more like sense- 

 organs ; he points out that externally they have 

 strong convex chitinous coverings which he does not 

 consider to be suitable for sucking purposes. Von 

 Schaub f talks of the two pairs referred to by Haller 

 as so-called suckers ; and is of opinion that they are 

 not suckers, although he draws an internal muscle to 

 each much the same as Nalepa's ; but Schaub considers 

 that a third pair lying between the other two, and 

 which he calls chitinous rings, are true suckers ; he 

 apparently only figures these in the d . 



With regard to my own observations on structure I 

 confess that in all my sections of the Tyroglyphidse so 

 very little is disclosed as to that of these so-called 

 suckers, and that little is so unsatisfactory, that I 

 should hesitate to come to any definite conclusion re- 

 garding the function (Nalepa says that it is very 

 difficult) ; but in Thy as petrophilus (one of the Hydrach- 

 nidae) the case was quite different ; there the organs 

 were large and highly developed, and I got beautiful 

 sections which I figured ; certainly the impression left 

 on my mind was that Haller was correct in saying that 

 the organs (in that family) appeared much more like 

 sense-organs than suckers. 



The principal difficulties in the way of considering 

 these organs to be suckers appear to me to be as 

 follows : 



FIRSTLY, that although the mode of coition of the 

 Oribatidge is still unknown, that of the Tyroglyphidse 



* " Die Hydra clmiden der Schweiz," in ' Mt. Ges. Bern/ for 1881, 

 published 1882, Heft 2, p. 48. 



f" " Ueber die Anatomic von Hydrodroma (C. L. Koch) : ein Beitrag 

 zur Kenntniss der Hydrachnidcn," ' IS. B. Ak. Wien,' 1688, Bd. xcvii, 

 Abth. i, p. 143. 



