122 C. E. Gordon — Early Stages in Paleozoic Corals. 



support of this interpretation ; the possibility of acceleration 

 makes the inference logical.* 



If these two septa were called into being at a relatively 

 early period, that is, before they normally would appear in a 

 non-accelerated type, it is easy to conceive how, once estab- 

 lished, this acceleration, as the name implies, would cause 

 these septa to appear at an earlier and earlier stage until in a 

 later geological type they would appear in the early nepionic 

 stages so fully developed as to present the character of prim- 

 ary septa. Their true nature then, in the absence of a series 

 showing this progressive acceleration, could be explained by 

 noting the subsequent development of secondary septa that 

 were not accelerated, and, in this connection, noting the final 



Figures 17 and 18. A portion, in each case of figures 7 and 14, with new 

 lettering. 



position of the septa that were accelerated, as I have done. 

 Duerden's figures, to my mind, lend themselves in every 

 respect to this interpretation. 



At the risk of repetition I have at this place introduced a 

 portion, in each case, of figures 7 and 14 with new lettering, 

 which may serve to recapitulate and make a little clearer the 

 foregoing discussion. 



Figure IT shows in a diagrammatic way the value of the 

 septa as interpreted by Duerden in figure 7. (P y ), " cardinal 

 septum " (Duerden) ; (P x ) " counter septum " (Duerden) ; (P) 



* The suggestion of Boveri that the anomalous number of the septa of the 

 first cycle in Tealia crassicornis may be explained as due to the precocious 

 development of four septa belonging to the second cycle, is a recognition of 

 the fact that acceleration in development may operate to conceal a primitive 

 condition. Boveri's suggestion is supported by his own observations on the 

 peculiar mesenterial arrangement in an undetermined larval form. (This 

 suggestion was not seen until this article was written.) 



