78 SECTIONAL ADDRESSES 



from the upper part of the Jamesoni zone of the Lower Lias up into the 

 Margaritatus zone of the Middle Lias. These are characterised by 

 shells that are closely coiled and are very inflated. Associated with these 

 are a number of variations which are less closely coiled and not quite so 

 inflated. In the Ibex zone and the lower part of the Davcei zone occur 

 forms, of the genus Androgynoceras, in which the inner whorls are not 

 inflated, and are ornamented with stout ribs, and possess that cluster of 

 features which characterises the Capricorn ammonite. The outer whorls 

 of these, however, revert to the condition seen in Liparoceras. In the 

 upper part of the Davcei zone forms occur in which the Capricorn 

 condition extends into the adult stage to the complete exclusion of the 

 Liparoceras combination of characters from the life-history. It seems, 

 therefore, that the Capricorn condition enters the stock as a set of new 

 characters in the early neanic stage of development of the early genera- 

 tions and proceeds during evolution through late neanic stages to the 

 adult in subsequent generations. Other features, such as the forward 

 bend of the ribs on the venter, so characteristic of Otstoceras, and the 

 deep lateral lobe in the suture line of Becheiceras, he assures me likewise 

 put in their first appearance in early development and subsequently invade 

 the later growth stages of succeding generations. 



It may be noticed that the extension of the new features into later 

 developmental stages is accompanied by a corresponding delay in the 

 time of appearance of the older features. This latter phenomenon was 

 also observed by Buckman, who proposed for it the descriptive term 

 ' Bradypalingenesis ' (1920). So near was he, and yet so far away from 

 realising that some principle other than recapitulation was at work in 

 development and evolution. 



Deuterogenesis and Tachygenesis {the appearance of new characters at the 

 latest stage in development and their extension to earlier stages). 



Looking at the facts of recapitulation from the prospective point of 

 view it will be realised that new trends of change, exhibited by the various 

 gentes discussed in the former part of this address, show themselves for 

 the first time in an incipient form in the adults of earlier species, and 

 become increasingly emphasised in the adults of subsequent generations. 

 Meanwhile the incipient phase passes by an acceleration of develop- 

 mental processes (tachygenesis) into the early life of these generations. 

 In other words, new characters, or rather trends of change, may enter 

 the stock in the later stages of development, and the changes passed 

 through in development in later generations go beyond and overlap those 

 seen in the earlier. This mode of entry of new characters may be 

 described as deuterogenesis in contradistinction to coenogenesis. 



There is no need to describe specific examples of deuterogenesis in 

 detail, since every case of recapitulation looked at prospectively provides 

 all that is required. Thus in the gens Z. delanouei, etc., the shortening of 

 the cardinal septum starts in the adult of Z.parallela, and the shortening 

 of all the septa starts in the adult of early forms of Z. disjuncta. Similarly 



