SOO. SOORPIONS sAND MITES: 
(ARACHNIDA). 

ORG) iro rE, Fes: A RUAN Es TDi pAc 
NOTHER class of animated beings now comes before us, which, under the general 
term of Arachnida, comprises the Spiders, Scorpions, and Mites. 
These beings breathe atmospheric air, they have no antennee, and they have 
four pairs of legs attached to the fore parts of the body. 
In some of the higher Arachnida, there is a bold division into thorax and 
abdomen, and the former portion of the body is clearly divided into separate 
segments. By the earlier naturalists, the Arachnida were placed among the 
insects, but may readily be distinguished by several peculiarities. In the first place, they 
have more than the normal number of six legs, which alone would be sufficient to separate 
them from insects. They have no separate head; the head and thorax being fused, as it 
were, into one mass, called the cephalo-thorax. In many of the lower species there is not even 
a division between the thorax and abdomen ; and the body, thorax, and abdomen are merged 
into one uniform mass, without even a mark to show their several boundaries. They undergo 
no metamorphosis, like that of the insects, for, although the young Spiders change their skin 
several times, there is no change of form. 
Beginning with the true Spiders, we find that their palpi (/.e. the jointed antenne-like 
organs that project from the cephalo-thorax) are more or Jess thread-like, and in the males are 
swollen at the extremity into a remarkable structure, as indicative of the sex as is the beard 
of man, the curled tail-feathers of the drake, and the gorgeous train of the peacock. In the 
different genera, these palpi are differently formed, and afford valuable indications for system- 
atic zoologists. 
Several examples of these Spiders will be described in the course of the following pages. 
They are remarkable through their exceeding diversity of form, and they can be readily 
distinguished from each other. They are very small, and the largest specimen is hardly equal 
to the head of a minikin pin. Still, their structure is not very difficult to be comprehended, 
and a moderately good magnifying-glass will mostly be sufficiently powerful to answer the 
purpose. The Spiders all breathe by means of certain lung-like organs, called the pulmonary 
sacs, though some species are also furnished with air-tubes. These sacs communicate with the 
external air by means of small apertures called ‘‘ stigmata,’ which are analogous to the 
spiracles of insects. There are seldom more than two of these stigmata, and never more than 
four. 
In these strange creatures, the mandibles are furnished with a curved claw, perforated at 
the extremity, something like the poison-fang of a venomous snake, and used for a similar 
purpose. A gland furnishes a secretion which is forced through these organs, and is injected 
into any object that may be wounded by the sharp claw. The fluid which is secreted for the 
service of the fangs is nearly colorless, and is found to possess most of the properties that 
exist in the venom of the rattlesnake or viper. The very existence of this fluid is denied by 
some writers, and its poisonous nature by others. I can, however, state from personal experi- 

