62 PROFESSOR OSKAR CARLGREN ON THE GENUS PORPONIA 



of the tentacles does not seem to show the displacement seen in Porponia ; in fact, 

 as far as I can see, the tentacles are at no places grouped in such a way that two 

 tentacles of the first order border on a tentacle of the second order, even though 

 certain changes in the size of the tentacles have been observed, so that accord- 

 ing to R Hertwig the exoccel-tentacles are not the smallest in size. Though 

 Actinernus plebeius and A. tuberosus do not suggest any close relationship to 

 Porponia, it is yet not impossible that the type specimen of the Actinernus genus 

 may show greater similarities, a question I may leave unsettled at present, as I have 

 not had the opportunity to examine this specimen.* 



For the present, therefore, we must be content with a comparison between 

 Halcurias, Porponia, and Synhalcurias. The question is now, where we are to place 

 these genera, and would it be of advantage to separate them from other forms 1 

 M'Murrich in 1901 dealt with this question with regard to the genus Halcurias. 

 " There are, apparently, three courses open for the disposal of the genus. It may be 

 referred to a family already existent, the definition of the family being changed, if 

 necessary, to accommodate it, or it may be taken as the type of a distinct family, as 

 Carlgren has done, or, finally, it may be separated altogether from the Hexactinise 

 and regarded as the type of a separate tribe. It seems to me that this last procedure 

 is quite unnecessary and would probably be entirely out of harmony with the phylo- 

 genetic relationship of the genus. We have learned within recent years how extensively 

 nearly allied forms may differ, and how great all the modification which the hexactinian 

 type may undergo. The entire facies of Halcurias is that of an hexactinian." I am 

 entirely in agreement with the above citation from M'Murrich, and, like this author, 

 I am of opinion that it is unnecessary to set up a separate tribe for this genus and 

 Porponia, as the whole development indicates that the initial stage is a typical 

 hexactinian with six pairs of mesenteries. M'Murrich comes further to the conclusion 

 that Halcurias need not be placed either in a separate family, as 1 had done in 1897, 

 but considers it preferable to refer the genus to the family Actinidse (Antheadse). 

 "The peculiar mode of development of the secondary and tertiary mesenteries is of 

 minor importance, and I see no more reason for separating Halcurias as the type of 

 a new family than I do for separating an octamerous sagartian or one with a multi- 

 plicity of mouths and many siphonoglyphs from the rest of the members of that family." 

 He supports this view because "occasional endocoelous development of mesenteries 

 have been already recorded, as in Bunodes thallia, in Actinioides dixoniana and 

 papuensis" — a condition already pointed out by me in 1897. 



But is this view of M'Murrich justifiable ? So far as I can understand, this is not 

 the case, as variations irregularly arisen through asexual propagation, or through 

 regeneration and regulation in the symmetry of certain species — in the case of the 

 phylogeny — cannot directly be compared with similar variations from the normal type 

 arising during the ontogeny — a condition not hitherto taken into consideration, but 



* Compare Appendix ! 



