474 G. HERBERT FOWLER. 



Granting, then, the evolution of a four-rayed stage from a 

 hydriform ancestor, and its further advance into an eight- 

 rayed organism, from which branched the five great groups of 

 Anthozoa already mentioned, we may conclude, at any rate 

 until a good explanation is forthcoming of the apparent dis- 

 crepancy between the larval types shown in Figs. A, B, and C 

 (pp. 470-71), either (i) that, if the first eight mesenteries of the 

 various larvae are homologous structures, and indicative of an 

 eight-rayed ancestor, this homology does not extend to their 

 musculature, and that mesenteries formed after the first eight 

 are not homologous with mesenteries of similar position in 

 adults whose larvae are of difi'erent types ; or (ii) that, if the 

 first twelve mesenteries are homologous structures, they may 

 arise in any order, and this order is not of homologous or of 

 phylogenetic significance; or (iii) that slightly diverging types 

 have reconverged in our present group of Hexactinise. All three 

 conclusions appear to me to be almost equally difficult of accept- 

 ance, although the third becomes less improbable when the 

 facts are considered (1) that this group, at first sight so homo- 

 geneous, is being constantly shown to include Actiniaria which 

 do not conform to the hexameral type; (2) that the order of 

 development of the mesenteries has been efficiently studied in 

 only about eight genera. The improbable conclusion drawn 

 above may therefore be expressed in this way, that both from 

 embryology and from morphology comes evidence to show that 

 the group Hexactiniae includes two or more groups, not clearly 

 distinguishable in the present state of our knowledge. 



When dealing with questions of this kind, in which the evi- 

 dence is obviously incomplete, a writer can but express his 

 personal beliefs ; but, while he cannot claim for them the 

 weight of admitted truths, he is allowed to apply them provi- 

 sionally in that capacity. On this score the beliefs which I 

 have stated — (1) that mesenteries are to be regarded as having 

 arisen primarily in connection with digestive cells, secondarily 



its branches ; both families have axial (superior) aud abaxial (inferior) direc- 

 tives at the ends of the long axis of the stomodseum, an orientation similar 

 to that of the polyps of Alcjouium. 



