PERIPATUS. 335 



in the Devonian period, it is reasonable to suppose that other 

 insects, besides forms like cockroaches, must have inhabited 

 the dry land of the Silurian period. 



While true scorpions have been found in the Upper Silu- 

 rian rocks of Scotland, Sweden, and New York, the oldest 

 insect-remains are the wing of Palceoilattina douviUei, an 

 insect probably allied to the cockroach, and found in the 

 Middle Silurian rocks of Prance. 



In the Devonian of St. Johns, N.B., have been discovered 

 fragments of the wings either of a May-fly or dragon-fly, and 

 five other species of doubtful position. 



In the Carboniferous formation insect-remains are more 

 numerous; they belong to the Thysanura, Orthoptera, May- 

 flies, dragon-flies, Heniiptera, with composite forms {Euge- 

 reon) and genuine Neuroptera, allied to Sialis and Corydalus. 

 No insects with a complete metamorphosis (except the Neu- 

 roptera) are yet known to have lived before the Mesozoic age. 



Class I. — Malacopoda {Peripatus). 

 Characters of Malacopoda. — This group is represented by 

 a single animal, the strange Peripatus of tropical coun- 

 tries, in which the body is cylindrical, the integument, an- 

 tennae, and limbs soft, not chitinized, with the head not 

 separate from the body, and bearing a pair of many-jointed 

 extensible antennae, with two pairs of rudimentary jaws 

 (mandibles and maxillae), and from fourteen to thirty-three 

 pairs of feet. There is a pair of nephridia to each segment. 

 It differs from other Arthropods in the two widely separated 

 minutely ganglionated nervous cords sent backward from the 

 brain; also in the minute, numerous tracheal twigs arising 

 from numerous minute oval openings (rudimentary spiracles) 

 situated irregularly along the median line of the ventral 

 surface of the body. The feet are soft, fleshy, and end in 

 two claws. Peripatus is viviparous. According to the 

 description and figures of Mr. Moseley, the young develop 

 much as in the chilopodous Myriopods {Oeophilus), show- 

 ing that Peripatus is nearer to the Myriopods than any 

 other group. That it is a tracheate animal was also proved 

 by Mr. Moseley; but owing to the nature of the nervous 

 system, the minute tracheae and their numerous irregular 



