C. E. Gordon — Early Stages in Paleozoic Corals. 121 



corallum. There they are, and if they do not show by their 

 presence a primary hexameral arrangement some very strong 

 evidence must be brought forward to show why they do not. 



I am aware of the difficulty of explaining away their very 

 apparent primary character, especially as any perfect series of 

 fossil forms is not at hand to give us the absolute proof that L. 

 prolifertwi may be at the extreme end of an accelerated series 

 in which the pair of " primary " septa under discussion appear 

 at progressively earlier and earlier stages in the life history of 

 the individual until at last in L. proliferum we have them 

 established so early that they simulate the nature of primary 

 septa. In my criticism of Duerden's paper I wish to accord 

 the author the credit due his careful investigations and to 

 acknowledge his wide acquaintance with the Anthozoa. I 

 would be understood in offering any other interpretation of 

 his figures than that which he gives as being conservative, and 

 far from committing myself as to having settled the matter. 

 At the same time I believe that such an acceleration, difficult 

 as it might be to account for, is far from being impossible, if 

 it is not quite probable. In the absence of definite proof we 

 have to rely upon analogy to a large extent, and call to our 

 service in interpreting the structures in L. proliferum the 

 knowledge furnished by studies upon other forms. 



The idea of acceleration is 'by no means a new one. The 

 principle undoubtedly has been an all important factor in 

 bringing about those mutations which are the true species in 

 certain evolutional series. In fact, it seems to be An many 

 cases the only means of interpreting certain aberrant indi- 

 viduals which are so often grouped together in a heterogene- 

 ous way. We may be unable to explain why certain structures 

 appear earlier in the life of certain individuals than they did 

 in -ancestral forms; but it is undoubtedly to be explained in 

 many cases as a reaction towards its environment on the part 

 of the individual, the response being a new anatomical struc- 

 ture, or a different plan of development because of a new 

 importance of old structures, such as the assumption of a 

 greater physiological importance of certain ones. On this wise 

 it would not be difficult to imagine that for some reason or 

 other, obscure as that may be, the mesenteries next the " cardi- 

 nal " septum in Duerden's figures are really secondary septa 

 called into being so early as to appear to be primary septa. 

 The striking resemblance of Duerden's figures, if I may again 

 call attention to this fact, to the usually accepted Zaphrentoid 

 type of arrangement and the fact that the so-called primary 

 septa follow the well recognized law of Kunth, are offered in 



Am. Jour. Sci. — Fourth Series, Vol. XXI, No. 122.— February, 1906. 

 9 



