36 RELICS OF PRLMEVAL LIFE 



Jelly-fishes. If, with some naturalists, we regard the 

 Sponges as very humble members of the coral 

 group (Coelenterata), then we have a right to add 

 them to its representatives in the lowest Cambrian ; 

 but perhaps they had better be ranked with the 

 next and lowest group of all — the Protozoa. 



These are the humblest of all the inhabitants 

 of the sea, presenting very simple, jelly-like bodies 

 with few organs, but sometimes producing complex 

 and beautiful calcareous and siliceous coverings or 

 tests. Animals of this type have been found in the 

 Lower Cambrian, though not in such vast multitudes 

 as in some later formations. There are also in the 

 Cambrian some large, laminated, calcareous bodies 

 (Cryptozoon of Hall), to be noticed more fully below, 

 and which have recently been traced in still lower 

 deposits even below the lowest Cambrian (Figs. 7, 8). 

 These have some resemblance to the layer-corals or 

 stromatoporae of the Silurian and Ordovician, which 

 are by many regarded as the skeletons of coral 

 animals of a low type ; but the microscopic struc- 

 ture of Cryptozoon rather allies it with some of 

 the larger forms of Protozoa found higher up in 

 the series of formations. We shall have to discuss 

 this later in connection with still older fossils. 



