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V . — Notes on New Acarelli. By J. Gr. Tatem. 
Plate XL. (Upper portion). 
In exhibiting balsam-mounted slides of new species of Acari, I wish 
to call the attention of the members to a fact of great significance 
in the life history of the creatures, and one, too, of much value 
generically considered. We all know that the young of the Acarine 
division of the Arachnid family are excluded from the ovum in an 
immature condition, possessing but three pairs of legs, though they 
acquire the normal four pairs after one or more subsequent moults. 
The common harvest bug, of which the adult form has yet to be 
recognized, is but a too familiar example of this hexapod stage of 
Acarine existence. The subjects I have embalmed have, however, 
entered upon the mite world in a still more imperfect state— they have 
but two pairs of legs ! — but to prove that they would ultimately be 
as capable as any of their congeners of exercising four pairs, they 
have two posterior pairs neatly packed up in their trunks ready for 
evolution in the progress of growth ! 
Two years since, at the July meeting of the Entomological 
Society, Professor Westwood gave descriptions of two species of 
minute four-legged Acari, the one detected in the unopened buds of 
black currant trees, the other in pustules on the leaves of pear 
trees, referring also to a third which had been previously found in 
France. He considers them a distinct tribe, and that they must at 
all events be placed in a separate genus, for which he proposed the 
name of Acarellus. To this group our specimens unquestionably 
belong, and although their obviously imperfect development more 
than justifies the suspicion that the genus is based on immature 
forms alone, it still constitutes a good and natural division of the 
family. 
In that example to which I have ventured to assign the specific 
name of A.pulicis, Plate XL. (its habitat having been the abdominal 
cavity of a dead flea), the hinder pairs of limbs are almost perfectly 
and completely formed, but still included within the cephalo-thorax, 
evidently awaiting the nearly approaching moult for extrication ; 
while in the other, which on like grounds I have called A. muscse, 
Plate XL. (detected clinging tenaciously in company with half-a- 
dozen others to the thorax of a small dipteron), the hinder pairs are 
more rudimentary, and with its much smaller size indicates an earlier 
stage of existence and more remote ecdysis, In both instances, 
however, it is quite apparent that in the process of development 
they would sooner or later have transferred themselves from the 
new genus Acarellus to that of Acarus proper. 
Of their life histories I have no knowledge. Discovered by 
accident, and not until after many hours of maceration in liq. potassm, 
