TRIASSIC PERIOD. 421 



But, although relics of Insects and of Crustaceans other than Ostra- 

 coids are rare, several species of these classes of Invertebrates, and 

 also of Worms, are indicated by the tracks which they left on the 

 material of the finer shales. Figs. 633-637 represent some of these 

 footmarks. Those of Insects were probably made by larves which 

 live in water, like those of many Neuropters. Nearly thirty species 

 of Articulates have been named by Hitchcock from the tracks. 



The Vertebrates thus far made known from their fossils and foot- 

 prints outnumber all other kinds of animal life ; and many were 

 of remarkable size. They include not only Fishes and Reptiles, but 

 also the first of Birds and Mammals* Thus the sub-kingdom of 



Hymenopters have four membranous veined wings, the anterior the larger ; 

 as the Bee, Wasp. 



Dipters have two membranous wings ; as the House-fly. 



These are the more common of the grand divisions of Insects. The Hy- 

 menopters are regarded as highest in rank. The Lepidopters, Dipters, and 

 Hemipters have sucking mouths; in the other tribes mentioned there are jaws. 



* With this first appearance of Mammals in the Geological history, a general 

 view of the classification of this class is here presented. 



Among Mammals there are three prominent groups : — 



1. Man, who stands apart from the rest. 



2. True viviparous tribes (or non-marsupial), including all ordinary Mammals, 

 as the Monkey, Lion, Elephant, Ox, Whale, Bat, Mouse, etc. 



3. Semi-oviparous tribes (mostly marsupial), in which birth takes place before 

 the maturity of the young, as in oviparous animals, and including the Opossum, 

 Kangaroo, Ornithorhynchus, etc. They are the lowest of Mammals. The mar- 

 supial species are so called because they have a pouch (in Latin marsupium) 

 below, for carrying the immature young. 



This third group is to some extent parallel in its series of species with the 

 second, or non-marsupial; that is, there are Carnivores, Herbivores, Insecti- 

 vores, Rodents, etc., in both groups, — so that the tribes of Mammals are repre- 

 sented under both types. 



The non-marsupials, or higher Mammals, contain in themselves two distinct 

 and parallel series, corresponding to two grand divisions : — 



1. The Megasthenes (from neya;, great, and aQevog, strength). — The superior type, 

 based on a larger and more powerful type of structure or life-system, as the 

 Monkey, Lion, and other Carnivores, Ox, Elephant, and other Herbivores, Whale 

 and other Mutilates. 



2. The Microsthenes (from uixpog, small, and aOevog). — The inferior type, based 

 on a small and weak type of structure or life-system, as the Bat, Hedgehog, 

 and other Insectivores, Mouse and other Rodents, Sloth and other Brutes or 

 Edentates. 



The parallelism between the two groups is complete. The Bats in the latter 

 represent the Monkeys in the former, the orders having so close relations that 

 they follow one another in Cuvier's classification ; the Insectivores represent the 



