130 ZOOLOGY. 



(^j>?, TS, fig. 45 ah c d e)\ LacJiesis perversa i^])!. 78, fig. 47) ; Ulohorus 

 walcnoirius {pi. 11-, fig. 57 «, and jp?. 7S,fig. 48); Tetragnatlia argyra {pi. 

 77, /i7. 54). 



The papers of Prof. IsT. M. Ilentz, on the spiders of the United States, 

 may be consulted in the Boston Journal of Xatural History. 



Class 5. Myriapoda. 



The Articulata of tliis class bear a close external resemblance to worms, 

 having a lengthened multi-articulate wingless and cylindrical or depressed 

 body, and numerous articulated feet, whence they derive their scientific 

 name as well as their common designation of centipedes and millipedes. In 

 the Chilopoda {centipedes) there are generally one, and in the Chilognatha 

 {millipedes) two pairs of feet to each segment, and they are usually termi- 

 nated by a simple claw. In the former order they are lateral, and in the 

 latter they are placed more towards the middle of the body beneath. In 

 certain accidental cases, there may be three pairs of feet to an odd segment. 

 The number of feet varies from twelve pairs to upwards of three hundred 

 pairs. 



The Myriapoda are terrestrial, living in dark and damp places, among 

 moss, or under bark and stones, some feeding upon animal food, and others 

 upon fungi, fruits, or decaying vegetable matter. They differ from insects 

 in the nature of their metamorphosis, being born without members ; but the 

 first moult exposes the head, antennae, and three pairs of feet, the second 

 moult exposes seven j^airs of feet towards the anterior part of the body, and 

 finally, with the sixth moult, the full number of feet and segments is 

 acquired, although the generative organs are not developed for two years 

 subsequently. These facts were ascertained upon the genus lulus., by Savi, 

 & distinguished naturalist of Bologna. 



Some of the species are luminous at night, at certain seasons or under 

 certain circumstances, and some secrete a penetrating, pungent, and dis- 

 agreeable material with an acid scent, although with neither acid nor 

 alkaline qualities. Gervais ascertained that species of Geopliilus will live 

 2. day or two in water, and that parts of the body will stir after being sepa- 

 rated two weeks. Some species are pretty widely spread, Scutigera 

 coleoptrata being found from the North of Europe to Egypt and Barbary ; 

 and it is found in the United States, where it has probably been introduced 

 by shipping, according to a suggestion of Say. 



This class is placed between the Arachnida and Insecta, by Latreille, in 

 his last work (Cours d'Entomologie), although his opinion had varied pre- 

 viously. There are certain analogies between the Annelida and the 

 Myriapoda, as in the genus Peripatus of the former and Polyxenus of the 

 latter, the fascicular sette of which resemble those of some of the Annelida. 

 Their affinity to the Crustacea is observable upon comparing forms like the 

 terrestrial geniLs Oniscus., and Gloraeris., which has a similarly shaped body, 

 the power of rolling itself into a ball, a crustaceous exterior, and similar 

 334 



