The Brain in the Oribatidse , &c. By A. D. Michael. 275 
degree of excellence which it has now arrived at ; and these minute 
Acari, which are possessed of a chitinous exo-skeleton, almost as hard 
and as brittle as glass (a peculiarity noticed long ago by v. Siebold *), 
had baffled my attempts to get any sections of them which were at all 
satisfactory or reliable ; and it is by sections that most can be learned 
respecting the brain and nerves of such extremely small animals. I 
allowed the matter to rest, hoping that improvements in apparatus 
and technique might some day enable me to do what I had not 
succeeded in doing at that time. The difficulty still exists, the chitin 
is so hard and brittle that instead of being properly cut, it either 
takes a notch out of the edge of the razor, or else breaks into 
numerous pieces at the first touch of the edge, and some of these 
pieces being carried before the razor, are apt to tear and destroy the 
soft internal organs which we wish to see ; nor have I found softening 
agents of any service ; if eau de Labarraque or eau de Javelle be 
employed I have found that the internal organs are destroyed before 
the chitin is softened. In spite of these difficulties I have by the 
skilful assistance of Mr. M. J. Michael of Davos, and with the aid of 
modern improved microtomes, been able to obtain some sections which 
at all events show what the brain is really like a great deal better 
than can be done otherwise ; and as there are not, as far as I know, 
any existing records on the subject, except the very imperfect infor- 
mation which will be found in my own works above referred to, 
I think it may be worth while to notice the brain, although I am not 
able at present to follow it up, as should be done, by a description of 
the nerves which proceed from it. The reason of this inability is 
somewhat strange ; it is simply that I have not, as yet, succeeded in 
seeing these nerves in any way fit for reliable investigation. It is 
curious, that even the larger nerves, such as those innervating the 
legs — which are easily seen, and are even conspicuous, in many 
Acarina far more sluggish than the Oribatidm, which, although, 
rather slow in their rate of progress, are not really sluggish animals — 
are difficult, or impossible to see in the Oribatidse ; even when one 
does get a good series of sections, or a good dissection, of the brain. 
Thus, in the crawling Water-Mite Thy as, which will be referred to 
later on, not only are the nerves to the legs large and easily traceable, 
but I have been able to distinguish and follow the very much smaller 
nerves to the mandibles, dorso-ventral muscles, and many other quite 
fine nerves, besides the more substantial ones to the palpi and eyes ; 
yet Thyas is a creature living under stones in the water, or in chinks 
of the rock, and moving but little, while most of the Oribatidae are 
fairly active creatures. The nerves of the latter must be very 
delicate to escape observation, they ought at all events to be seen 
where they start from the brain if they were not of extreme tenuity. 
* ‘The Anatomy of the Invertebrata,’ English translation, Boston, 1854, p. 3G8, 
note 1. 
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