British Orihatidee. By A. B. Michael. 35 



many species, are apt to get almost obliterated, the skin puffing up 

 into an arched form ; this does not occur in all instances, but it 

 does so frequently enough to make it wise, whenever a nymph has 

 been drawn or described from an inert specimen, to record the fact. 

 Another change in the nymph as it matures is that it is usually 

 whiter and softer at first than in the more advanced stages ; as a 

 rule it becomes a little harder and darker with each change of 

 skin, but it never becomes anything approaching as hard or dark 

 as the perfect creature, and some species do not get at all darker 

 during the nymj^hal stage. The chitinous exo-skeleton appears to 

 develop first on the cephalo thorax and 'legs, particularly on the 

 anterior dorsal surface of the former. The abdomen does not ever 

 assume a chitinous appearance in any nymph that I have observed. 

 When the perfect creature first emerges from the nymj^hal skin it 

 is generally somewhat light coloured and soft looking, and it is often 

 some hours before the full hardness and darkness are acquired. 



It seems to me that when the life-histories are fully known, 

 they will probably be of service in determining whether the genera 

 into which the Orihatid/e have usually been divided are natural or 

 only artificial groups; thus, in some strongly marked genera, as 

 for instance Nothrus and Bamseus, the nymph is usually suffi- 

 ciently like the perfect creature to enable the observer to predict 

 with some confidence what the nymph will turn out to be, indeed 

 in most instances the resemblance is very close in these two 

 genera. In other strongly marked genera, as Orihata, Tegeo- 

 cranus, Leiosoma, &c., the nymph is so difierent that it would be 

 impossible to make any guess whatever from resemblance to the 

 adult ; but in some of these genera, as Orihata, there is a certain 

 pervading character about most of the nymphs which would give 

 an indication of the genus they belong to. On the other hand, in 

 the genus Pelops, the separation of which from Orihata depends 

 upon highly artificial distinctions, the nymphs have much the same 

 leading feature as in Orihata. In the genus Hoplophora, which is 

 undoubtedly a natural group, the nymphs have a strong likeness 

 to each other; there are other genera in which no rule can be 

 traced, but it remains to be seen whether these will eventually 

 turn out to be difierentiated by distinctions of importance. 



Another interesting point, which one observes in studying the 

 immature forms of the OrihatidcT, is that in the earliest stages tlio 

 abdomen often exhibits decided traces of segmentation ; these 

 usually vanish with advancing age, so much so indeed that the 

 unsegmented abdomen is a characteristic, not merely of the family. 

 but of the order ; the segmentation has not, in any instance that 1 

 have seen, proceeded to the extent of making one segment movable 

 upon the other, but is still sufficiently marked to be distinguisliable. 



1 have mentioned above that the change from nymph lu 



D 2 



