4 8 



CERIANTHARIA. 



Finally I give p. 4447 in tabular form a synopsis of those morphological facts in the adult 

 Ceriantharia, which have been more thoroughly studied anatomically, and may now be grouped fairly 

 correctly in their systematic relations. The species I have had occasion to examine are distinguished 

 by spaced type. The species of Arachnactis of which I have given a detailed account are also in- 

 cluded in the table subjoined. As appears from these, there is still a good deal to be added from 

 an anatomical point of view before several of these species can be characterized quite satisfactorily. 

 As the species I have myself investigated have been treated throughout in the same way, the ana- 

 tomical account of them is more complete than in the case of the others, whose organisation I have 

 built up from the accounts of publications, whose statements on the homology of the mesenterial 

 appendages in particular, are often very obscure. 



Section IV. 

 On the morphology of the Ceriantharia. 



Since in my opinion the morphology of Ceriantharia, in spite of the researches of various in- 

 vestigators, is still inadequately worked out, I give here a general survey of the most important of 

 the morphological facts found within this group of animals. In this survey I take account principally of 

 such organs as shew more or less variation of structure and arrangement in the different species, 

 and for that reason are of service for purposes of classification. In the following comparative view 

 of the morphology I have chiefly taken into consideration such species as I have myself investigated. 

 Above all I have treated in special detail the mesenterial filaments and their appendages, which in 

 Ceriantharia present a very different appearance and structure in the different species. 



1 . Arrangement of the tentacles. 



The tentacles in Ceriantharia are arranged, as is well known, not only marginal but also labial. 

 The arrangement of these tentacles differs according to the size of the species and according to age. 

 The simplest grouping is found in the small species A rachnanthus oligopodus (and sarst?) and in Botru- 

 cnidifer norvegicus, where the labial tentacles are arranged in a single row, which is also the case with 

 the marginal tentacles of the former. In larger species as in C. membranaceus, lloydii, P. multiplicatus, they 

 are arranged in three or four cycles. As a typical arrangement in a larger species may be taken the 

 grouping in C. mcmbranaceus. That this arrangement only appears late in the course of the develop- 

 ment, may be seen in C, lloydii, very young specimens of which only have the tentacles arranged in a 

 row. In larger specimens on the other hand three, and in larger still, four cycles are found. It clearly 

 follows from this, that the tentacle arrangement in the same species may alter and that rearrangements 

 in the form of displacements take place during growth. In particular the zone about the directive 

 chamber, where the tentacles as a rule shew a different arrangement from nearer the multiplication 

 chamber, is remarkable for somewhat variable tentacle attachments. In the main however the grouping 

 of the tentacles in the larger specimens is similar. Yet it is noticeable that certain labial tentacles 



