76 SECTIONAL ADDRESSES 



do not undergo further expression or change. In the case now to be 

 considered they extend gradually into later stages. Recently Schindewolf 

 in Germany and Spath in England have done good service by emphasising 

 the existence of palaeontological evidence for characters appearing coeno- 

 genetically and extending, in subsequent generations, through later stages 

 into the adult. In 1925 Schindewolf proposed the term ' proterogenesis ' 

 for this principle of ontogenetic anticipation. In 1933 he wrote a fuller 

 account of the principle and furnished a number of examples of his own 

 as well as from other writers. 



The conception that the larval characters may exert an important 

 influence upon adult organisation is not a new one. It is indeed familiar 

 to biologists under the heading of paedomorphism. It was also dimly 

 foreshadowed in the writings of much earlier workers. Thus for example 

 Haeusler (1887), dealing with certain foraminifera of the family Miliolidce 

 from the Lias of Banbury, showed that forms, now referred to the genera 

 Nodobaciilaria, Ophthalmidium, Spirophthalmidium, form a series ranging 

 from the condition in which the shell is straight, except for the be- 

 ginnings of a coil at the embryonic end, to one in which the whole shell 

 is coiled. He ventures to suggest that the first is the more primitive 

 condition and that, during evolution, the process of coiling extended into 

 later and yet later stages until it eventually dominated the whole shell. 

 It should, however, be noted that he produced no evidence for the 

 actual sequence in time of these members of this series, and it will be 

 shown later that a quite different explanation is feasible. 



Schindewolf, in a treatise which deals with this subject at some length, 

 assembles a variety of illustrative examples. They are a mixed lot and 

 include some which do not really exemplify the principle he is discuss- 

 ing, but, as will be shown later, belong to a quite different category. 

 For the present our attention must be limited to genuine cases of pro- 

 terogenesis (paedomorphism), that is, to cases in which new characters 

 appear early in development and extend during evolution into later life. 



The simplest, clearest, and at the same time the most fully authenticated 

 example which Schindewolf describes is yielded by fossils from the 

 Ordovician rocks of the Scandinavian Baltic belonging to the nautiloid 

 family of the Lituitid^. The central genus Lituites is characterised by 

 the fact that while the major portion of the shell is straight, the early 

 formed portion is coiled. On the basis of the principle of recapitula- 

 tion it has usually been assumed that Lituites was the retrogressive 

 descendant of a completely coiled ancestor. Schindewolf, however, 

 describes a series of forms (Fig. 3) which commences in the Vaginaten 

 Kalk with the genus Rhynchorthoceras in which the shell is wholly straight 

 or only slightly curved. This is followed in the Platyurus Kalk by a 

 variety of forms, including Lituites itself, which exhibit various degrees 

 of coiling. The series ends in the Chiron Kalk in Cyclolituites in which 

 the shell is almost completely coiled. 



Other examples quoted by Schindewolf are far from being convincing. 

 Reference to a paper on certain foraminifera by Rhumbler (1897) from 

 which he culls several cases reveals a flimsiness of stratigraphical evidence 

 which rules them out of court for any serious discussion of the problem. 



