PRIMITIVE ANIMAL FORMS 121 



The Sea-anemones of our coasts are coralozooids that have 

 lost the faculty of producing lime, a property that permitted 

 the other coral-building organisms to play a tremendous part 

 during the Geological Periods, and which still makes them 

 important agents in modifying tropical coasts. In the present 

 state of almost all coralozoids, the dactylomerids associated 

 with the gastromerid number either six or a multiple of six. 

 This number may remain fixed or may augment during the 

 animal's life. The phenomena of embryogenetic acceleration 

 which I have discussed elsewhere, 1 show how the Madrepore 

 corals constructed on the sextuple type were able to give rise to 

 the Coral and to animals which form with them the order 

 Alcyonaria. These animals appear at a first glance to be 

 Madrepora constructed on the eightfold type, but in reality 

 they are quite different. 



From the point of view of the history of the development of 

 life on earth, we will draw from the foregoing these few con- 

 clusions only : alongside of the Sponges and the Bryozoa, which 

 appear to have but little plasticity, the Polyps were very 

 rapidly evolved ; obviously their primitive forms can only 

 have been Hydromedusae, but from these arose simultaneously 

 the parallel forms Acalephas and Corals. Although actually 

 free, the Acalephas must have appeared originally in sedentary 

 forms, which developed by branching. They acquired their 

 liberty secondarily, and only, as we have seen, through the 

 agency of tachygenesis. 



While these organisms were evolving from the fixed merids 

 others were developing from the free merids. These last appear 

 to have belonged exclusively to the type provided with a general 

 cavity, which when they attached themselves to some 

 object, gave rise to the Bryozoa. There was no reason why 

 the preservation of their liberty should have deprived them of 

 their faculty of budding. Locomotion, however, is a factor 

 which has completely modified the conditions of evolution. 

 In fact, when the initial merid remained free and moved about, 

 its weight, locomotion, and the conditions of its search for food, 

 compelled it to abandon a form symmetrical upon one axis, such 

 as it could have retained if it had always swum suspended 

 in the water, and take on a form symmetrical to a single plane. 



1 XLIII, 753. 



