66 SECTIONAL ADDRESSES 



however, seems to necessitate a modification in the statement of that 

 principle, for in this case the resemblance is not limited to organisms 

 lower down in the scale, but extends to embryos of corals of later date 

 and more advanced structure. Indeed, so far as it goes, the evidence 

 indicates that this embryonic combination of features is one which may 

 be characteristic of the whole class Anthozoa. Though Von Baer, like 

 modern biologists, had in mind only contemporary animals, the facts 

 show that the principle is applicable to forms belonging to different 

 periods of time. 



No doubt in the development of Zaphrentis there were, as in other 

 Coelentera, yet earlier stages, starting with the fertilised egg and passing 

 on to a free-swimming larva, which of necessity are beyond the ken of the 

 palzeontologist. Keeping these in mind, as well as those discussed above, 

 we may distinguish in the life-history of this, as indeed of other organisms, 

 two main phases in development : the embryonic and the neanic re- 

 spectively. The former covers a series of changes leading up from a 

 single cell to a condition which, notwithstanding its relative complexity, 

 has little or no resemblance to the adult but which, nevertheless, provides 

 the basis out of which the adult may be produced. The latter covers 

 that series of changes in the course of which the features which characterise 

 the adult gradually emerge and ultimately attain full expression. These 

 phases overlap one another and in so doing exhibit stages which are 

 transitional in character between the two. In Zaphrentis the stages 

 leading up to and including the corallum with six septa almost radially 

 arranged belong to the embryonic phase. The immediately succeeding 

 stages, during which the tetrameral symmetry is being established, are 

 transitional. Those leading from this point onwards to the adult belong 

 to the neanic phase. 



In the embryonic phase the combination of characters seems to have 

 attained a state of stability that furnishes a plan of structure which is 

 common to widely separated members of the class. It must be regarded 

 as the culmination of a long process of evolution of embryos in which 

 many factors which concerned adult life have played no part, but in which 

 factors foundational to adult development have been preserved. So far 

 as known this embryonic condition in Zaphrentis bears no resemblance to 

 the adult condition of any coral stock that could be regarded as ancestral 

 to this genus. The features concerned in this ancient and stable com- 

 bination appear to me to conform to those ' primitive types of structure ' 

 for which Garstang (1921) proposed the term ' palasomorphic. ' Should 

 advancing knowledge bring to light adult fossils of an earlier ancestral 

 stock and possessing these same features, then this term would have to 

 give place to Haeckel's term ' palingenetic,' which Garstang rejects. This 

 problem will demand very careful investigation. Thus, for example, the 

 extraordinary resemblance between the attached dipleurula of echino- 

 derms and the fossil Aristocystis among the blastoids may, apart from the 

 presence of plates in the latter, be taken as recapitulation of adult 

 characters. On the other hand the conditions of the resemblance may 

 have arisen, .not in the adult but in the larval blastoid. 



In the neanic phase the organism exhibits a combination of less stable 



