THE BEGINNING OF LIFE ON THE EARTH. 33 



or less distinct granular appearance. Many of them show a 

 distinct spot or cell, called the nucleus, and some have minute 

 transparent vesicles, which contract and expand alternately, 

 and appear to be of the nature of circulatory or excretory 

 organs. They have no proper alimentary canal, but receive 

 their food into the general mass and digest it in temporary 

 cavities. Their means of locomotion and prehension are 

 soft thread-like or finger-like processes, extended at will 

 from the surface of any part of the body, and known as 

 false feet (pseudopodia). From these processes the whole 

 group has obtained the name of Rhizopods, or root-footed 

 animals. They may be regarded as constituting the simplest 

 and humblest form of animal life certainly known to us. 



The very numerous species of these creatures existing in the 

 waters of the modern world may be arranged under three prin- 

 cipal groups. The first and highest includes those which have 

 lobate or finger- like pseudopods, and a well-developed nucleus 

 and pulsating vesicle (Fig. 20, a). They are mostly inhabit- 

 ants of fresh water, and destitute of a hard crust or shell. A 

 second group, including many inhabitants of the sea as well as 

 of fresh waters, has thread-like radiating pseudopodia 1 (Fig. 

 20 b). Some of these form beautiful silicious skeletons. A 

 third group, essentially marine, consists of those with reticulated 

 pseudopodia, and usually destitute of distinct nucleus and pul- 

 sating vesicle (Fig. 21). They produce beautiful calcareous 

 skeletons, often very complex, or sometimes are content to 

 cover themselves with a crust of agglutinated grains of sand. 

 It is to this last group that Eozoon belongs, and to the highest 

 division of it — that which has the shell perforated with minute 

 pores, often of two kinds. It is curious that just as we have 

 the chambers and pores of Eozoon filled with serpentine, 

 so in all geological formations and in the modern seas it 

 is not uncommon to find Foraminifera having their cavities 



* Sometimes separated as a dii;tinct order under the name of Radiolaria. 



