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 pnrt 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 wliat 

 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 m(;tamorphosed remains of For an tin if era. 



The beds of chalk which underlie the nummulitic lime- 

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

 tical with the Glohlgerina ooze, the species of Globigerina 

 found in it being indistinguishable from those now living. 

 The remains of l<ora7ninifera 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 Eozoi'm 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 hils 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 : 



" Petref'aeta non a calcc, seel calx a petrefactis. Sic lapulca ah aniniallbus, 

 nee vice versa. Sic rupes saxei non primievi, sod temporis filia?." 



And there mav 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 ENDOrLASTICA. 



1. The Radiolakia. — Most species of the genus Actino- 

 phrya or " sun-nnimalculo," which is common in ponds, are 

 simply free-switnmino; mvxopods with stiffish pseudopodia, 

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

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



