3516. Body thick, mostly globiform; head and thorax blended together; only four pairs of feet.
Fam. 4. Brachiopodoid, Acarides.
Body rounded; all three parts confluent; usually only two simple eyes. The Acari are mostly so small, that their parts can only be distinctly seen through the microscope. Their mouth is always very much arrested, and has maxillæ, which are in some cases adapted for manducation, in others for suction.
Fam. 5. Pteropodoid, Scorpions.
Body tolerably cylindrical, and all three parts connate; palpi very large and forcipiform.
Fam. 6. Sepioid, Spiders.
Body rounded, head and thorax connate, abdomen separate, mostly eight simple eyes.
Their most remarkable organs are the four spinnerets in front of the anus, which probably stand in the signification of the renal organs, just as the material of the Spider-threads does in that of the urine.
The tracheæ are but few in number, and expand into lung-like vesicles.
The sexual parts do not lie posteriorly by the anus, but at the root or base of the abdomen.