256 PROFESSOR OSKAR CARLGREN ON THE GENUS PORPONIA 



tion with each other. M'MuRRicn is therefore quite right in saying that a genus or 

 species need not be separated from other genera or species because it has been trans- 

 formed into an 8- or 10-rayed type. It must be pointed out, however, that such a type 

 may in certain cases be of great importance for the classification, namely, in cases where 

 8 or 10 rays are observed in all species of a certain genus, as the variation in the 

 symmetry can naturally be used as a good generic character. We know of no case 

 where a number of the pairs of mesenteries differing from 6 has led to the setting up of 

 a separate family. 



As shown above, both Porponia and Halcurias, from an assumed typical 6-paired 

 mesentery stage, are transformed into one having 10 pairs of mesenteries. Where the 

 transformation takes place in the ordinary manner by the belated appearance of certain 

 mesenteries in certain areas and through the arising of other mesenteries in the 

 exocosls,* it seems unnecessary to separate these genera, but as the 10-rayed condition 

 arises in such a specific way by development of mesenteries in the endocoals, a develop- 

 ment that is continued during the following cycle, I consider it absolutely necessary to 

 set up a separate family for these genera, the more so as such an ontogenetic develop- 

 ment of mesenteries in the endoccels has not been observed in any other Actiniaria of a 

 higher type. As far as we know, no such displacement of the tentacles has been 

 observed in other forms of Actiniaria than the above mentioned. I place Porponia and 

 Halcurias together in one family, therefore, to which already in 1897 I gave the 

 appropriate name of Endocoelactidse. 



III. RELATIONSHIP OF THE FAMILY ENDOCCELACTID^E TO OTHER 

 ACTINIARIA ORIGIN or THE RUGOSA TYPE. 



As already mentioned in the introduction, R. HERTWIG stated the possibility that 

 Porponia, owing to the arrangement of the macro- and micro-mesenteries, might form a 

 transitional stage between the Hexactiniaria (Actiniaria) and Zoanthidse (Zoantharia). 

 This explanation of the position of Porponia and the family Endoccelactidse cannot, 

 of course, be maintained, after we have ascertained the facts on which the relation- 

 ship between stronger and weaker mesenteries depends. There is nothing in the 

 organisation of the family Endocoelactidse that might indicate a close relation to the 

 Zoanthidse, as the development of the mesenteries in this family takes place in quite a 

 different way from that in the latter characteristic group of Anthozoa. 



In my paper on Endoccelactis ( = Halcurias} I pointed out that in Minyas there is 

 a strong tendency to widen the endoccels at the expense of the exoccels, causing an 

 alteration in the grouping of the mesenteries, which had some resemblance to the 

 alteration in the grouping of the 10 stronger mesenteries in Endoccelactis. How this 

 grouping of the mesenteries has taken place in Minyas is still unknown, but it may 

 possibly have arisen in connection with the development of mesenteries in the endocosls, 



* It is also to be noted that not all 8- or 10-rayed types are homologous with each other, for the 8- or 10-rayed 

 condition is not always obtained in the same way ontogenetically. 



(ROY. SOC. EDIN. TRANS., VOL. L., 64.) 



