42 
FIRST ANNUAL REPORT OF THE 
as they progress, after the fashion of antennae. Now in Insects, where the head and 
thorax are always distinct, as the antennae always grow out of the head and the legs 
out of the thorax, there can be no possible confusion between leg and antenna, no 
matter what the function of the leg may be ; because, if the organ in question grows out 
of the thorax, it is to be considered as a leg, even if it discharges the duties of an 
antenna. But in Mites, where the head and thorax are confounded together, just as 
they are in a Crab, or a Lobster, or a Crawfish, the inexperienced observer, although 
none of the great Class to which the Mites belong have any antennse at all, is yet very 
apt to consider the front pair of legs as antennae., whenever he sees them used as an¬ 
tennae. Consequently, as a general rule, the easiest mode for beginners to distinguish a 
Mite from a true Insect is, to see whether the animal under examination has a distinct 
head or not. If it has, it cannot be a Mite. If it has not, it cannot be a true Insect. 
So far we have been talking about the structural peculiarities of the perfect Mite and the 
perfect Insect. In the larva or imperfect state the case is somewhat different. Just as, 
in the larva state , many Insects have legs so minute that they are scarcely distinguishable, 
others again Jiave no legs at all, others again, in addition to the six normal jointed legs, 
have at their tails a sham leg (or “ pro-leg ”) or fleshy excrescence not divided into joints 
like the true legs, but still performing the same functions as they do, and others again 
have from four to sixteen of such sham legs strung along the hinder part of their bodies, 
besides having the normal six true legs in front; so, in the larva state , many Mites have 
only six legs, although, when fully grown, they acquire an additional pair. In this case, 
as these Mite-larvae are always exceedingly minute in size, it is sometimes not very easy 
to distinguish them from the similarly minute larvae of certain Bark-lice and Plant-lice, 
to which they bear a strong general resemblance. There is, however, one distinctive 
character by which, so far as a pretty extensive observation goes, I believe that the very 
young six-legged oval larvae of the Mites may be always readily distinguished from the 
very young six-legged oval larvae of the Bark-lice and the Plant-lice. In the two latter 
groups the three pairs of legs are always equidistant, or nearly so, from each other, at 
their origin on the the lower surface of the body. In the former group the two front 
pairs of legs are placed close to one another on the lower surface of the body and not 
very far from the front end, while the hind pair of legs are placed wide apart from the 
others and not very far from the hind end. In a somewhat wide experience with these 
creatures, I have met with no intermediate grades whatever in these very remarkable 
characters. 
Of course, as the larvae of all Bark-lice and Plant-lice have antennae, and those of 
Mites have none, if you can make out the antennae clearly in the larvae that you have 
under examination, they cannot be Mite-larvae. But as the larvae of Bark-lice and 
Plant-lice very frequently do not raise up their antennae as they crawl along, and as the 
legs can generally be made out pretty distinctly whenever larvae of any kind are crawl¬ 
ing along, characters drawn from the legs are evidently the most generally available. 
The number of distinct species of Mites to be found in the United States is rather 
large, but still very greatly inferior to the number of distinct species of Insects found 
within the same limits. Unlike the true Insects, they are all of them quite small in 
size, the largest Mite known to me being much less than one-tentli inch in length. 
They swarm everywhere ; but their Natural History is so far almost entirely a sealed 
book to the scientific world, because no one hitherto has devoted his exclusive attention 
to them. I am myself acquainted with no less than twenty distinct species, that form 
curious “galls,” or unnatural growths, upon the leaves of various trees. One of these 
