Study of Madreporarian Types of Corals. 227 



within the group of Madreporaria during the course of the 

 geologic ages. Some of the more important and general of 

 these evolutionary changes may be shortly enumerated : — 



(1) TahulcB became modified centrally as columella and 

 pseudocolumella, more seldom became vesicular. 



(2) Instead of one to four basal pits (fossulaj) for the recep- 

 tion of specialized reproductive mesenterial filaments, the 

 whole base of the calyx became deepened^ usually around the 

 axial columella or pseudocolumella. 



(3) Septa became more prominent and exsert in growth ; 

 their structure became more elaborate, their surfaces fluted 

 and richly granulated, their edges knobbed, toothed, serrated, 

 spined. 



(4) The " rugose epitheca " became tardy in growth, and 

 was replaced functionally by a theca or pseudotheca. 



(5) Vegetative increase was facilitated by the specialization 

 of an " edge-zone " around the polyp (represented by the 

 " costate " portion of a calyx, or its ancient homologue, the 

 peripheral " dissepimental zone" of Cyathophyllids). 



(6) The ^'"'pinnate insertion''^ of septa demonstrated by 

 Kunth in primitive corals became gradually a feature of 

 embryonic calyces, and then vanished ; but the embryonic 

 mesenteries appear in recent types in tlie same " tetrameral " 

 order as the septa did in the mature calyces of primitive types. 

 The disappearance of " pinnate insertion " as a generic feature 

 did not necessarily entail the abandonment of a tetrameral, 

 more properly said bilateral, arrangement of the septa. It 

 induced mainly the hastening of septal insertion^ the relative 

 position being often retained^ even in adult forms *. Again, 



many recent types said to have radial symmetry of septa in 

 adult calyces have well-marked bilateral symmetry in the 

 young individual. 



All the above changes indicate, in the author's opinion, 

 merely various lines of adaptivity, correlative with one great 

 leading change in the living polyp — an increase in the number 

 of gonad-beariny mesenteries and in the musculature of the 

 mesenteries^ resulting in improved powers of self-preservation 

 and of reproduction. 



The evolution of recent Madreporariau families from primi- 

 tive types hinges round the gradual incoming of that main 

 change. The general law of the hastening of the develop- 

 mental stages in. the individual worked with this change, and 



* Various observations bearing out this statement have been made by 

 the author on Mesozoic corals. These are fully described in the author's 

 " Monograph of the Upper Jurassic Stramberg Corals," at present being 

 published in the ' Palaontologische Mittheilungen ' (Koch, Stuttgart). 



