30 
A short Description of an Acarus and its Agamic 
Reproduction."^ By Richard Beck. 
(Read December 13th, 1865.) 
After keeping one or two species of acarus for a very con- 
siderable timCj and having no difficulty in increasing or 
diminishing their number according to the treatment I 
pursued^ it was much to my surprise when about the middle 
of last summer they began rapidly to disappear, and in a 
comparatively short time I was quite unable to obtain from 
the whole of my stocks any living specimens. 
On one occasion, when making a general search to see 
whether the acari had merely moved their quarters, I found 
in the thread of a spider's old cocoon a species of acarus, so 
entirely different from those I was looking for, and pre- 
senting to me such novelty in appearance that I lost no time 
in carefully securing this and one other specimen which were 
all I could find ; one of these, however, was injured in its 
capture, and died immediately. 
The general appearance of the one still left was that of a 
female, but without a male I thought there would be no 
chance of obtaining any reproduction of its species, and I had 
moreover no clue to the food it required. Instead, however, 
of following the often too hastily adopted plan of merely 
making a mounted preparation of my specimen, I determined 
to preserve its life as long as possible, and I am now not only 
enabled to prepare a specimen whenever I like, but also to 
supply some facts as to its life-history which could only have 
been obtained by keeping it for some considerable time in a 
living state. 
The question of food puzzled me for some time, as I 
naturally confined myself to obtaining supplies from the 
locality where I found the acarus, but a part of the cocoon, 
the eggs of a spider, and their first cast skins, were all alike 
refused. It was only as a last resource and judging from the 
remarkable size of its falces, together with its peculiar move- 
ments, that I gave it some living acari of a different species, 
these I soon saw were quickly seized, the disappearance of 
my colonies of acari which I have mentioned was at once 
explained, and I continued to supply my new specimen with 
food, hoping it would turn out to be an impregnated female. 
In a few days it laid some eggs, and these duly hatched, 
* Since reading this paper Mr. Bockett has shown me a specimen of the 
same acarus, mounted by J. Bourgoine, of Paris, which he names "Cheyleius 
des pilleteries (rare)." 
