592 TEE POPULAR SCIENCE MONTHLY 



cent., or 115,000 species, live in the sea, and 71,000 have their habitat 

 on the land or in the waters of the land. Of the 115,000 kinds of 

 known animals inhabiting the seas nearly 70 per cent, are Ccelenterata, 

 Echinodermata, Molluscoidea and Mollusca, the types of organisms 

 most often found by the stratigrapher and on which he is largely de- 

 pendent in deciphering the ancient geography. 



Let us now examine into the number of available fossil forms made 

 known by the paleontologists. As early as 1868, Bigsby in his 

 "Thesaurus Siluricus" listed 8,897 species from the strata beneath 

 the Devonic, and in his " Thesaurus Devonico-Carboniferous " of 

 1878, he further enumerated about 5,600 Devonic and 8,700 Carbonic 

 forms. In 1889 Neumayr concluded that there were then known about 

 10,000 Jurassic species. We may therefore estimate that the paleontol- 

 ogists of to-day have access to at least 100,000 species of fossils. Their 

 numbers in the geologic scale are about as follows: Cambric 2,000, 

 Ordovicic 8,000, Siluric 8,000, Devonic 9,000, Lower Carbonic 7,000, 

 Upper Carbonic 8,000, Permic 4,000, Triassic 6,000, Jurassic 15,000, 

 Cretacic 10,000 and Tertiary 25,000. The end of species-making is 

 not at all in sight, and the day will come when paleontologists will deal 

 with ten times as many species as are now known. 



Stiles tells us that zoologists know but from 10 to 20 per cent, of 

 the living forms, and there should therefore be from 3,760,000 to 

 4,700,000 different kinds of animals alive to-day, ranging from the 

 protozoa to man. Now let us compare the abundance of living ani- 

 mals with those of the geologic ages, and especially with the Jurassic 

 period, of which life we have probably a better knowledge than of any 

 time back of the Tertiary. The European Jurassic has long been 

 divided into 33 zones (Buckman hints at a probable 100), and if we 

 hold that each one of these times had only one quarter as many species 

 as in the lowest estimate of the present world, there must have lived 

 during the entire Jurassic something like 31,000,000 kinds of animals. 

 Yet paleontologists have described not more than 15,000 Jurassic 

 forms. The great imperfection of the extinct life record is thus forcibly 

 brought to our attention, and we learn from these estimates that for 

 each kind of animal preserved in the rocks more than 2,000 other kinds 

 are utterly blotted out of the geologic record. 



Much of this more apparent than real imperfection, however, is 

 due to the vast number of insect species now living — animals that must 

 have been comparatively few in the Jurassic, due in the main to the 

 absence of flowering plants. From these figures, however, we must not 

 conclude that the geologic record is equally imperfect throughout; for 

 the paleontologist studying marine fossils well knows that he can not, 

 as a rule, hope to study other than those kinds of animals that have 

 hard and calcareous or siliceous external or internal skeletons. Of 



