OCTINEON LINDAHLI. 475 



with reproductive cells and concentrations of muscle-fibres; 



(2) that the eight-rayed larval stage is of phylogenetic value ; 



(3) that any of these eight or of subsequently formed mesen- 

 teries may be specialised for the performance of one function, 

 digestive, reproductive, or muscular (whether protractor, re- 

 tractor, or depressor), and may drop one or both of the other 

 functions — may now be applied to Octineon. 



At first sight this Actiniarian fits perfectly into Professor 

 McMurrich's scheme, taking a place immediately above the 

 Edwardsise, at the point where (inter alias) the lines of 

 descent of Hexactinise and Zoanthese diverge — a stage at which 

 mesenteries 5 and 6 of Fig. A (p. 470) are throughout life less 

 developed than the remaining eight primary mesenteries (cf. 

 McMurrich's table, ' Journ. Morph.,' v, 150). Against this 

 view I would urge that the numerous mesenteries of lower 

 orders in Octineon are not incipient mesenteries, 'prophetic 

 germs' of greater efficiency to come, but rather retrograde or 

 arrested mesenteries, which have (phylogenetically speaking) 

 lost their filaments, reproductive organs, and (most of their) 

 muscle-fibres, in correlation with the extraordinary muscular 

 development of ten primaries. The fact that the " pairs " are 

 apparently not always of equal breadth (age) or length, and 

 that some of them die out to reappear at a lower level — that 

 they are, in fact, very irregularly developed — is an additional 

 argument in favour of this view. It can hardly be denied 

 that this degradation is true of mesenteries 5 (fig. 12) if this 

 figure be compared with an ordinary Hexactinian diagram, 

 and these are structurally identical with those of the lower 

 orders. Further, if the shifting (p. 467) of the eight retractor 

 muscles were to be carried a stage beyond its present condition, 

 the eight mesenteries which are at present connected with them 

 (1, 2, 4, 6, fig. 12) would be reduced to the same degraded 

 type. Lastly, if the suggestion made above as to the origin of 

 mesenteries be true, and they are all in the first instance 

 physiologically equivalent, the mere fact of enormously in- 

 creased efficiency in a few will surely lead either to the 

 gradual obliteration of the rest, or to their adaptation to new 



