CHAP. XIX - Functions and Instincts. Arachnidans, Pseudarachnidans, and Acaridan Condylopes

Summary

Having wandered long enough, perhaps too long, in a wide and mazy field, but fertile everywhere in proofs of the Power, Wisdom, and Goodness of the Creator, it is time to return to the high road from which we diverged.

The Class of animals which led me into this digression were the Myriapods, concerning which I observed, when I commenced my account of them, that on quitting the Crustaceans, the way seemed to branch off from the long-tailed Decapods by them, and from the short-tailed ones by the Arachnidans. We are now then to give a history of the latter Class.

Latreille, in which he has been followed by most modern Arachnologists, in his work in aid of Cuvier's last edition of the Règne Animal, divides his Arachnidans into two Orders, Pulmonaries, or those that breathe by gills, and Trachearies, or those that breathe by spiracles in connection with tracheæ. In his latest work, which he did not live to finish, he added a third Order, including some parasites, infesting marine animals, such as the whale louse. These, from their having no apparent respiratory apparatus, he named, Aporobranchians.

As the pulmonary Arachnidans of Latreille differ from the Trachearies, &c., not only in having their body divided into two sections, but likewise both in their respiratory organs and those of circulation, I have always regarded them as forming a distinct Class.