FOSSILS— THEIR NATURE AND INTERPRETATION. 99 



express the effects of struggle with environment more accu- 

 rately than do any others, for it is with the hard parts that 

 the animal has met environment, struggled with and resisted 

 it ; hence, fossils, so imperfect as evidence of the anatomical 

 structure of the organisms, are the best of evidence of the effect 

 of the interaction bctzveen the forces of ancestry, working 

 throtigJi the laivs of generation tending to repeat the ancestral 

 characters, and the forces of the environment ivorking tJirough 

 the lazvs of struggle for existence in modifying those characters 

 by adjustment. 



Kinds of Hard Parts of the Animal Kingdom preserved as Fos- 

 sils. — As we deal, then, with the hard parts only, a few words 

 will be said regarding the kind of hard parts which are found 

 in the several classes of the Animal Kingdom. 



We glance over the Animal Kingdom and see that there 

 are large groups of animals now living, which, if they were to 

 die and every advantage were offered for their preservation in 

 their natural habitat, would leave no trace of their existence 

 a year after their death. It is important, therefore, to learn 

 at the outset to what extent the paleontological record will 

 be found silent because of impossibility of preservation of the 

 evidence. 



Protozoa. — Among the lowest group of animals, the sub- 

 kingdom Protozoa, the Gregarinidae, found mainly within 

 other animals, would be absent because they form no hard 

 parts nor framework Avhich could be preserved. 



Among the Rhizopoda, differing from the former class in 



Fig. io. Fig. ii. 



Fig. io. — Foraminifera. Globigerina bulloides d'Orb. Miocene. (S. and D.) 

 Fig. II. — Radiolaria. Sticliocapsa Grothl KUst. Jurassic. (S. and D.) 



the possession of pseudopoda, and leading a more active and 

 independent life, the orders of Moiicra and Ama'ba, as far as 



