. Comparative anatomy. Anatomy, Comparative. THE ANIMAL KINGDOM 15 Class Arachnoidea This division of the arthropods, most of them air-breathing, but without tracheae, in addition to a vast number of minute creatures, contains the harvest men, the scorpions, and over ten thousand species of spiders all with four pairs of walking legs. The familiar horseshoe or king crab, Limulus, among the largest of arthropods, in length up to 50 cm. is the only surviving relative of the Paleozoic trilobites, which, in their day, dominated the sea. The newly- hatched limulus is strikingly like a trilobite; an
. Comparative anatomy. Anatomy, Comparative. THE ANIMAL KINGDOM 15 Class Arachnoidea This division of the arthropods, most of them air-breathing, but without tracheae, in addition to a vast number of minute creatures, contains the harvest men, the scorpions, and over ten thousand species of spiders all with four pairs of walking legs. The familiar horseshoe or king crab, Limulus, among the largest of arthropods, in length up to 50 cm. is the only surviving relative of the Paleozoic trilobites, which, in their day, dominated the sea. The newly- hatched limulus is strikingly like a trilobite; and yet, the limulus is clearly a much modified ^it^»ll»!Sfe^\M^«IH^»^ LIMULUS- AN ARACHNID Fig. 10.—A young Limulus viewed from the dorsal side. William Patten and Gaskell have attempted to demonstrate that this animal lies in the direct line of verte- brate ancestry. The Limulus has, moreover, a further interest, in that it also resembles, superficially, certain of the Paleozoic ostracoderms, a group which, it is maintained by Patten and Gaskell, contains the long-sought ancestor of all the vertebrates. Limulus belongs to the order Xiphosura (Mero- stomata). The Eurypterids are a closely related group of extinct paleozoic arachnids of large size. Class Tracheata In addition to the insects, all of which as adults have three pairs of walking legs, the group contains many difi^erent primitive forms which link the arthropods to the annelids. Of these forms, the most primitive is the genus Peripatus, with fourteen to forty-three pairs of legs, and so strange a body that it has been taken both for a mollusc and for a worm. The familiar centipedes and myriapods have from a dozen to nearly two. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Her
Size: 1949px × 1282px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
