Further Notes on British Orihatidse. By A. D. Michael. 5 



opening, the folding doors which close these respective apertures 

 having also dropped off. Sometimes the apertures are so small, or 

 the larvae so large, that they cannot easily escape by the apertures, 

 . and I have more than once had to assist those I had bred in 

 confinement by breaking away the shell. 



Dr. G. Haller, of Bern,* lately recorded the finding of 

 numerous dried exo-skeletons of Soijlophora in winter among 

 the fallen leaves, each shell having a large single mature egg in it. 

 Haller concludes that the female Ho^lo2)hora, when about to 

 deposit an egg, seeks for the exo-skeleton of some deceased member 

 of its own species, and uses it as a shelter for the egg. It is of 

 course quite possible that this may be so — I cannot deny it — but, as 

 Haller does not appear to have seen the egg laid, and he was 

 hardly likely to have done so, as the Oribatidse object to light, I 

 cannot help thinking that this is probably another instance of the 

 fourth method above described, with the distinction that here only one 

 egg is matured at once. If it be not so, it is odd that the Hoplo- 

 phora should always choose the exo-skeleton of a Hoplophora 

 instead of distributing its favours more generally amongst other 

 genera. 



Deutovum Stage. 



Another observation which I have to record, is relative to the 

 development of the egg after extrusion. The eggs of some 

 Orihatidse are of a rather leathery consistency, those of other 

 species are provided with a hard chitinous shell, which is brittle 

 and non-elastic. Claparede, in his ' Studien an Acariden,' records 

 the occurrence, in the ova of Atax honzii, of what he calls a 

 deutovum stage ; Megnin has observed a similar thing in the case 

 of Tromhidium fuliginosum, and I myself noticed it in the ova of 

 other Trombidiidse, but I am not aware of any one having observed 

 it amongst the Orihatidse. I have now to record that it decidedly 

 is equally a portion of the life-history of some, but not of all, 

 members of this family. The deutovum stage is as follows : 

 When the exterior shell of the egg is hard and non-extensile, the 

 gradual increase of volume in the egg-contents produces so much 

 pressure from within upon the shell that the latter splits sharply 

 all round its periphery, dividing it into two somewhat boat-shaped 

 halves; the inner membrane which lines the shell has in the 

 meantime increased in strength, and has become the true en- 

 velope. The space between the two broken halves of the exterior 

 shell is at first a mere line, but, as the contents increase, this line 

 widens, and the halves of the old shell get pushed further and 

 further apart, showing a broad white space (the inner membrane) 



* "Miscellanea acarinologica," MT. d. Schweiz. entom. Gesellschaft, 1879, 

 No. 4, p. 502. 



