WIJJIIN THE GENUS DENDJIONEPH'J'HYA. 



41 



depend on conditions of growtii. On this view, tlie occurrence 

 of a species witli tlie same anthocodial armature in each of the 

 three groups would not mean that a similar speci:i,lization had 

 occurred three times on difterent lines of evolution ; it vuould 

 mean that one and the same species occurred in three diflerent 

 vegetative forms — Glomerate, Divaricate, and Umbellate, which 

 depended on gj'owth conditions. 



For various reasons this view is improbable :— (1) In many 

 cases the Glomerate, Divaricate, or Umbellate mode of growth 

 is clearly expressed in young forms 1-3 cm. high. (2) When 

 exactly the same anthocodial armature occurs in two or all of 

 the three groups, the two or three species in question differ in 

 other details, such as the length of the polyp stalk, the nature of 

 the supporting bundle, and the spiculation. This does not look 

 like the occurrence of the same species in three vegetative guises. 

 There are Umbellate colonies, however, which seem to pass 

 through a Divaricate stage when they are young and small, but 

 these are in my experience fewer than forms which are Umbel- 

 late from near the start. 



Text -figure 6. 





In support of the view that a colony usually shows vei y early 

 whether it is going to be Glomerate, Divaricate, or Umbellate, 

 I have given a series of diagrammatic representations of a 

 dozen small colonies drawn to actual size. . It goes without 

 saying that the definite architecture cannot be expressed until 

 there are quite a, number of polyps in the colony. But the limit 

 is uncertain. The central figure of the group depicts the 

 primitive, quite undifferentiated colony from which soon the 

 distinctive form embodies itself. Above it to the left are 

 Glomerates, to the right Umbellates, while below is a row of 

 Divaricates. 



§ 10. Starting with the Glomeratse, I suggest tliat the fol- 

 lowing should be regarded as illustrations of primitive types : — 



1 . In the savignyi group : — 

 D. argentea with irregular arrangement — most primitive of all, 



