AND RELATED GENERA, SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 255 



which I must strongly emphasise. A species, for example, that normally, through 

 unequal development of mesenteries, through stopping of the growth of certain parts 

 and more rapid growth of others during the ontogenic development, e.y. from being 

 a 6-rayed becomes an 8- or 10-rayed type, which is constant or nearly so for the 

 species, cannot in phylogenetic respects be compared with another species where the 

 same stages are obtained through accidental, asexual propagation or by regeneration. 

 In the first case, the 8- or 10-rayed type is constant for the species, and occurs onto- 

 geuetically and phylogenetically ; in the latter case, on the other hand, it is a mode of 

 adaptation in a less or greater part of the individual, and is dependent on the course of 

 the asexual propagation, and the greater or less reduction of the old mesenteries in the 

 separated or damaged fragments, a condition which has been further dealt with in my 

 studies on the regeneration and regulation stages in the Actiniae, 1904, 1909. In so 

 far as it has arisen ontogenetically, an 8- or 10-mesentery stage is thus of direct use for 

 the phylogeuy, but not in other cases. What applies to the occurrence of an 8- or 10- 

 rayed type of Actiniaria also applies to the varieties that arise through the develop- 

 ment of the mesenteries in the endocoals. In such cases the conditions are in full 

 agreement with those found in 8- or 10-rayed forms. Porponia and Halcurias leave 

 no doubt that the regular development of mesenteries in the endocrels has taken place 

 ontogenetically, whereas the irregular and chance development of mesenteries in the 

 endocoels in Bunodes, Actinioides, and others stands in intimate connection with the 

 regeneration or possible early dislocations of tissues during development. In Porponia 

 and Halcurias the development of mesenteries in the endocoels is of importance for the 

 classification, whereas the abnormal occurrence of mesenteries in the endocosls in 

 Bunodes, etc., is of no use for this purpose. 



The peculiarity that mesenteries occur regularly in the endocosls during the course 

 of development is thus quite specific for Porponia and Halcurias, and probably also 

 for SynJialcurias, and has not been observed in other Actiniaria. The question is still 

 left open, if this peculiarity is of such great importance that it necessitates the setting 

 up of a separate family. As mentioned above, M'MuRRicn connects the development 

 of mesenteries in the endoccels with the occurrence of an 8-rayed type, with the develop- 

 ment of several mouths and several siphonoglyphs. Just as little as we separate the 

 forms showing such variations from the normal Actiniaria type ought we, in his opinion, 

 to separate Halcurias from allied forms on account of the development of mesenteries 

 in the endocoels. That the multiplication of mouths in a genus of Actiniaria does not 

 involve a separation of the genus in question from other closely related species is 

 evident from the above, as this multiplication has not arisen ontogenetically, but by 

 asexual propagation. The same is certainly also the case with the multiplication of the 

 siphonoglyphs. It is now left to take into consideration the abnormal development of 

 the mesenteries. An 8- or 10-rayed type derived ontogenetically from a 6-rayed one is, 

 as already known, by no means a seldom occurrence within the Actiniaria group, and 

 may obviously arise within different families and genera that are in no genetic connec- 



(ROY. SOC. EDIN. TRANS., VOL. L., 63".) 



