228 A. D. MICHAEL ON THE ACARINA. 



genital organs is either at the side or on the superior surface of the 

 body. Fig. 4 (after Claparede), shows the dorsal aspect of the 

 male Myobia musculi, and exhibits the peculiar position of the organ 

 c, and its place of emergence, d. 



The last subject to which I will refer is the nature and structure 

 of the oviduct in the Oribatidce. As far as I am aware, the only 

 author who has noticed this organ (beyond stating the fact of its 

 existence) is Nicolet, who has figured it in Hermannia piceus (or, as 

 he calls it, H. crassipes), and when I say that it is done by Nicolet 

 it is equivalent to saying that it is done well, but it happens that the 

 organ is shorter and less developed in that species than in most of 

 the family, and, moreover, Nicolet does not describe the minuter 

 structure, which I have found specially interesting, he has 

 indicated it in his figure, but, as indicated it differs slightly from 

 that of the species in which 1 am about to describe it, and I doubt if 

 it would be understood from Nicolet's figure alone. The species I 

 have selected is Er emeus oblungus, one of my reasons for choosing 

 it is the great length of the oviduct, and another the greater trans- 

 parency of the chitinous exo-skeleton than is usual amongst the 

 Oribatidce which enables the observer to see the organ lying within 

 the body when not extended. 



The genital aperture in both sexes of the Oribatidce is usually of 

 a square, elliptical, or truncated conical shape, or some combination 

 of these forms, and is placed, as before stated, in the anterior part 

 of the ventral surface of the abdomen, and is closed by two chitinous 

 folding doors which exactly fit the opening. Within this aperture 

 the oviduct is attached, as shown in Fig. 7, pi. XIII. It is a long, 

 transparent, membranous tube, which, when fully extended, is, in this 

 species, longer than the whole length of the creature, but when not 

 in use it is wholly retracted within the body, and it is the peculiar 

 formation which allows of its being retracted to which I will now refer. 

 In the first place the tube, when withdrawn, appears to be drawn within 

 itself by introversion, but even this is not enough, for not only 

 would it be insufficient in consequence of the great length of the 

 organ, but also in order to allow the very large eggs to pass freely it 

 is necessary that the tube should be capable of expansion laterally as 

 well as in length. When I was examining the organ with a rather 

 low power (I think a half-inch) , my attention was called to the mode 

 in which this was effected by a play of iridescent colour. I at once 

 suspected that I was dealing with a lined surface ; a higher power 



