654 THE AMERICAN NATURALIST. | (VOL: XXXII. 
larger than earthworms, as in Phlegethontia of the Ohio and 
Ophiderpeton of the Bohemian coal measures. 
Already, then, in Permian times the stegocephalous type 
showed signs of long occupation, old age, and degeneration. 
The process of degeneration and reduction in, and loss of, limbs 
may have been initiated as far back as the closing centuries of 
the Devonian. i 
The effect of the Appalachian revolution and corresponding 
physical changes in Europe was by no means disastrous to the 
Stegocephala, for those of the Liassic, where the conditions 
must have been more formidable to terrestrial vertebrate life, 
were abundant, and in some cases at least colossal in size. 
Whether the salamanders, ceecilians, sirens, and Amphiuma of 
present times are persistent types, survivors of Carboniferous 
times, or whether the process of modification has been accom- 
plished a second time within the limits of the same class, is, 
perhaps, a matter for discussion. 
Besides the introduction and elaboration of the air-breathing, 
four-footed labyrinthodonts, the sloughs and sluggish streams 
were alive with Naiadites and its allies, forerunners of the 
Unionide, and with them lived shelled phyllopods, Estheria 
having already appeared in the Devonian, Leaia appearing in 
the Carboniferous; and also the larva of aquatic net-veined 
insects, fragments of the imagines of which were detected by 
Hartt at St. John, New Brunswick. 
The coal-bearing strata are largely fresh-water beds of fine 
shale, and well calculated to preserve the hard parts of delicate 
animals, but on general grounds it is evident that the great 
extent of lowlands with extensive bodies of fresh water com- 
municating with the shallow sea was most favorable to the 
development and differentiation of terrestrial life. Though 
fresh-water and land shells (pulmonates) appeared in the 
Devonian, they were apparently more abundant in the coal 
period. Especially rapid was the incoming of the arthropods ; 
both diplopods, some of them very remarkable forms, and 
chilopods lived sheltered under the bark of colossal lycopods P 
with them were associated scorpions, harvestmen, and spiders. 
The great profusion of net-veined insects discovered at Com- 
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