82 THE ANATOMY OF INVERTEBRATED ANIMALS. 



convert it into slate ; and thus, all the fundamental minerals 

 of which rock-masses are composed may have formed part of 

 living organisms, though no trace of their origin may be dis- 

 cernible in them in their final state. 



Paleontology lends much support to the view that what 

 is here suggested as a theoretically possible origin of much 

 of the superficial crust of the globe may have been its actual 

 origin. 



The nummulitic limestones of the Eocene epoch cover an 

 enormous area of Central and Southern Europe, North Africa, 

 West Asia, and India. And their chief mass is made up of 

 the more or less metamorphosed remains of Foraminifera. 



The beds of chalk which underlie the nummulitic lime- 

 stones, and occupy a still greater area, are essentially iden- 

 tical with the Globigerina ooze, the species of Globigerina 

 found in it being indistinguishable from those now living. 

 The remains of f oraminifera have been detected in the lime- 

 stones of all epochs as far as the Silurian, and Ehrenberg dis- 

 covered that an old Silurian green-sand, near St. Petersburg, 

 is composed of casts of Foraminifera just such as are now 

 being formed in the Gulf of Mexico. And if the Eozobn Cana- 

 dense be, as it appears to be, nothing but an incrusting form 

 of Foraminifer, the existence of these oganisms is carried back 

 to an epoch far beyond that at which any other evidence of 

 life has yet been found. So that it is possible that, as Wy- 

 ville Thomson has suggested, the enormously thick " azoic " 

 slaty and other rocks, which constitute the Laurentian and 

 Cambrian formations, may be to a great extent the metamor- 

 phosed products of Foraminiferal life. 



Hence the words of Linnaeus may be literally true : 



" Petrefacta non a calce, sed calx a petrefactis. Sic lapides ab aniinalibus, 

 nee vice versa. Sic rupes saxei non primsevi, sed temporis filise." 



And there may be no part of the common rocks, which enter 

 into the earth's crust, which has not passed through a living 

 organism at one time or another. 



II. THE EKDOPLASTICA. 



1. THE RADIOLARIA. Most species of the genus Actino- 

 phrys or "sun-animalcule," which is common in ponds, are 

 simply free-swimming myxopods with stiffish pseudopodia, 

 which radiate from all sides of the globular body. The sub- 

 stance of the latter presents one or more " contractile spaces " 



