﻿138 EVOLUTION IN THE PAST 



polyzoans Of polyzoans it may be remarked that the highly organised 

 colonies with zooids in lidded tubes, and with a depressed 

 class of slave-zooids (Cheilostomata), now far surpassed the 

 once dominant lidless colonies (Cyclostomata). The latter 

 showed no sign of changing their democratic character. 



sea-urchins Sea-urchins were not so diversified as in the last Period ; 

 but bilateral forms with the mouth well brought forward 

 were becoming predominant ; and some present-day genera 

 sea-lilies were beginning to appear (Hemiaster, etc.). Crinoids seem 

 once again to have been " minished and brought low." 

 corals Corals for the most part closely resembled some of the 

 forms now living. Solitary corals of existing genera were 

 numerous (Turbinolia, etc.). Reef -building was chiefly being 

 carried on by the Porites — a genus still prominent in coral 

 life. Of Madrepora corals — the most important of the reef- 

 builders at the present time — there is no evidence. 



protozoans Perhaps the most remarkable feature of Eocene invertebrate 

 life was to be found in the lowest division — the protozoans. 

 The wonderful amount of rock-building done in Cretaceous 

 times by these individually insignificant creatures has already 

 been referred to ; and the part played by them in the Eocene 

 was no less astonishing. On a great part of northern France, 

 then submerged, countless millions of foraminifers lived and 

 died (Miliola, etc.). In course of time their accumulated 

 shells resulted in the formation of thick layers of rock, now 

 known as Miolitic limestone. In modern times recourse has 

 been made to this vast and closely packed protozoan cemetery 

 for the building of many stately mansions. 



Another family of protozoans was in innumerable force 

 in the Mediterranean— a much larger sea then than now. 

 These rock-builders, on account of the coin-like form of their 

 shells, have been named Nummulites. They varied in 

 dimension from minute size up to that of a crown piece ; and 

 their shelly wealth is now known as nummulitic limestone. 

 Eocene nummulites are commemorated in the Pyramids^ 

 and also in mountains. The Pyrenees, Alps, Carpathians, and 

 Himalayas are all largely composed, even at their highest levels,, 

 of nummulitic remains. Those lofty ranges, therefore, cannot 

 have been raised above sea-level before the Eocene Period. 



