C— GEOLOGY 59 



well as in Haeckel's positions. The fundamental difference between 

 them and their philosophical descendants is that for the former it is a 

 recapitulation oi juvenile conditions, for the latter it is a recapitulation of 

 adult conditions. It will be helpful in further discussion if the two posi- 

 tions are referred to as juvenile and adult recapitulation respectively. 

 In both cases the recapitulation may be either specific or general. 



The main point at issue, therefore, is whether or not adult recapitulation, 

 either specific or general, does occur. Some thinkers, especially upon 

 the biological side, say emphatically 'No.' Others, especially invertebrate 

 palaeontologists, say ' Yes.' 



Morgan (1925), whilst apparently subscribing to what is here spoken 

 of as juvenile recapitulation, holds that adult recapitulation is quite ruled 

 out of court by the fact that variations are germinal in origin and dis- 

 continuous in mode of appearance. There must, however, be some 

 defect in his interpretation of the phenomena of variation, for, as will be 

 seen presently, many well-authenticated cases of adult recapitulation are 

 known. 



At this stage it is well to remind ourselves that even the most ardent 

 adult recapitulationist realises that the record is usually more or less 

 vitiated and incomplete. Haeckel himself, by the phrase ' abbreviated 

 repetition of phylogeny,' acknowledges that the record is curtailed. He 

 also recognised that it was subject to falsification by the appearance during 

 early life of features specially adapted to the conditions of life of the 

 embryo or larva. For this phenomenon he introduced the term ' coeno- 

 genesis.' As long as these features appeared to be limited in their influence 

 to the early developmental stages very little importance was attached to 

 them. In recent years, however, Garstang on the biological side and 

 Spath (1932) and Schindewolf (1925) on the palasontological side have 

 shown that their influence may extend in a marked degree even into adult 

 life, a process for which the last-named writer proposes the term ' protero- 

 genesis.' This discovery I fancy has played no little part in the recent 

 intensification of activity in undermining the pre-eminent position held 

 by the principle of recapitulation. 



In matters of this kind there is a danger lest we should slip into the 

 assumption that only one method has been pursued by Nature, but it is 

 surely a grave mistake to assume that she is so bankrupt in originality. 

 The fact that serious workers can hold such diverse views indicates the 

 possibility that Nature's methods are equally diverse. It seems appro- 

 priate therefore that an attempt should be made to re-examine the evidence 

 in the hope of gaining a clearer understanding of the relationships of the 

 various view-points to one another. From such a survey, geology as well 

 as biology has much to gain ; for as long as systematists drift along with 

 only a confused appreciation of the laws of development and evolution 

 they will be without fundamental principles to guide them in dealing 

 with the multitude of specimens which are coming, in ever- increasing 

 volume, from geologists in the field. 



Naturally my approach to this survey will be from the palaeontological 

 side, but I hope there is still enough of the zoologist left in me to enable 

 me to appreciate fully the more purely biological points of view. My 



