BIOCHEMICAL STUDIES OF PHYLOGENY 133 



normally placed in the family Suberitidae, a family containing only 

 saturated sterols. Bergman has shown that saturated sterols 

 are present in this sponge and therefore the sterol assay agrees 

 with its placing amongst the Suberitidae. Unfortunately the range 

 of sterols of the family Hymeniacidonidae is not yet known but 

 there is no reason why this sponge should be transferred from the 

 genus Hymeniacidon to that of Stylotella. Bergman states, " such 

 a transfer will remain premature until more is known about the 

 sterol contents of other species of Hymeniacidon and of the closely 

 related Halichondria " and he makes his position even more clear 

 in the statement, " It is dangerous and frequently misleading to 

 base significant conclusions concerning comparative biochemistry 

 on data derived from but a few representatives of a given phylum. 

 This point is apparent when the great diversity of sterols in 

 Porifera is considered." 



To return to the echinoderms it will be remembered that so far 

 only three types of sterol have been described in the literature 

 for the echinoderms. There is a likelihood that further study of 

 the echinoderms will show a greater divergence of the sterols 

 present in this group and that the cleavage shown in the table on 

 p. 131 will not be so clearly delineated. 



