. The origin and evolution of life, on the theory of action, reaction and interaction of energy. t these animals originate in armored land forms with a solid bonyshell, and pass from the terrestrio-aquatic into the littoral and then into the pelagiczone, in which the solid bony shell, being no longer of use, is gradually atrophied. Afterprolonged marine pelagic existence these animals return secondarily to the littoralzone and acquire a new armature of rounded dermal ossicles which develop on theupper and lower shields of the body. The animals (Sphargis) then for a second timetake up existence
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. t these animals originate in armored land forms with a solid bonyshell, and pass from the terrestrio-aquatic into the littoral and then into the pelagiczone, in which the solid bony shell, being no longer of use, is gradually atrophied. Afterprolonged marine pelagic existence these animals return secondarily to the littoralzone and acquire a new armature of rounded dermal ossicles which develop on theupper and lower shields of the body. The animals (Sphargis) then for a second timetake up existence in the pelagic zone, during which the dermal ossicles again tend todisappear. gidae), an extremely sj^ecialized type of sea turtles. It is be-lieved that after a long period of primary terrestrial evolution ^^^_^ ^__^ ii^ which the ancestors of these turtles acquired a firm,bony carapace for land de-fense, they then passedthrough various transitionsinto a primary marine phaseduring which they graduallylost all their first bony arma- FiG. 79. The Existing Leatherback ture. Following this sea. The Existing LeatherbackChelonian Sphargis. In this form the solid armature adapted to aformer terrestrial existence is being replacedby a leathery shield in which are embeddedsmall polygonal ossicles. After Lydekker. phase the animals returnedto shore and entered asecondary littoral, shore-liv-ing phase, also of long dur-ation, in course of which they developed a second bonyarmature quite distinct in plan and pattern from the first. AQUATIC REPTILES 203 Descendants of these secondarily armored, shore-living typesagain sought the sea and entered a secondary marine pelagicphase in course of which they lost the greater part of their
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