576 SYDNEY J. HICKSON. 



probable. Having formed communicatious of this nature 

 between the individual corallites, every intermediate condition 

 between this and the condition in which the pores are drawn 

 out into the form of hollow tubular communications or perfo- 

 rated platforms would be of advantage to the colony as afford- 

 ing more room for the development and growth of buds ; and, 

 indeed, as Professor Nicholson (19) has shown, every inter- 

 mediate condition can be found between the mural pores of 

 Favosites and the tubular communications of Syringopora or 

 the platforms of Chonostegites. 



Previously, however, to the Cornularia-like ancestor tliere 

 must have been a solitary ancestor similar to Haimea or Hartea. 

 The genus Sarcodictyou (Gosse, 7) consists of simple polyps 

 united together only by very delicate tubular threads. From a 

 condition of the stolon so simple as this there may have been 

 in the course of evolution two principal variations. Either the 

 thread-like communications increased in number and size and 

 underwent various anastomoses, forming a retiform stolon like 

 Syringopora, or else the threads may have become broader by 

 the growth of ooenenchym, and eventually formed a lamellar 

 stolon containing a network of canals, as in Cornularia and 

 Tubipora. Thus arranged in a tabular form the phylogeny 

 of the Stolonifera might be represented as follows : 



Tubipora 



Syringopora i'avosites-like ancestor 



Coruularia, Clavularia 



— Sarcodictyon 

 Solitary ancestor like Haimea. 



Before concluding this paper, I must acknowledge my in- 

 debtedness to Professor Moseley for much valuable aid and 

 advice, to my sister. Miss A. W. Hickson, for the most excellent 

 and valuable drawings represented by figs. 1 and 5si, and to 



