336 DEPARTMENT OF THE NATAL SERVICE 



8 GEORGE V, A. 1918 



fact, upon such little basis, makes it necessary to materially discount any argument 

 based on the statement. The resultant assertion depends for its value on the signifi- 

 cance of the word " distinct." According to the remainder of the paper it might better 

 have read " when otherwise the zooids present differences in the opercular apparatus ''' 

 but with such an interpretation every other taxonoraist will not necessarily agree. 

 Some of them may even have the temerity still to believe that there may be some cor- 

 relation between colonial and individual characters. 



Levinsen entirely neglects the systematic value of the characters of the gonosome 

 and hence in the genera in which he has introduced the most radical changes are to 

 be found the widest diversity in these characters. In the genus Sertularia " the gono- 

 thecse present a very different habitus, being either smooth, ringed or provided with 

 two or more spines" (p. 298), and in the genus Odontotheca "the gonothecse present 

 a very variable habitus, being either smooth, ringed or provided with two spines " 

 (p. 308). No system of classification based on colonial characters could present more 

 " distinct structural diversities " than this. 



With regard to the nature of the opercular apparatus almost anyone will adm:'t 

 that it is a good character, but even if it were the most suitable single character for 

 diagnosis, it would not signify that the whole classification must depend on it, since 

 there are other good characters. Levinsen says, " It seems reasonable to ascribe sys- 

 tematic significance also to the operculum, a structure that must be regarded as the 

 complement of the protective cases, and, so to speak, as the end result of the same 

 effort which led to the formation of the hydrothecse and gonothecte " (p. 288), and yet 

 in this classification all of the hydrotheca with the exception of the opercular apparatus 

 receives no consideration and the gonotheca is left out entirely. Farther on in the 

 same paragraph he says the operculum " has in common with other structures of 

 systematic significance, a rich development of characteristic modifications which give 

 excellent generic characters," but in his classification he has eliminated the consider- 

 ation of " other structures of systematic significance." 



It seems a very satisfactory character in one respect as any cases of disagreement 

 can be blamed on regeneration or injury but the very fact that regeneration is so very 

 apt to take place and that the apparatus is so delicate as to be so susceptible to injury, 

 makes its value for diagnosis of doixbtful significance. After one has spent as much 

 time and observation on the operculum as Levinsen did before writing this paper it 

 might be possible to judge the nature of the operculum correctly from the appearance 

 of the rest of the apparatus even when the operculum has been torn away but one with 

 less experience will certainly have serious doubts at times when the operculum is not 

 present and it is not always possible to have an unlimited supply of material to 

 examine for hydrothecae perfect in this respect. When Levinsen finds it necessary to 

 disagree with the interpretation put upon the nature of the opercular apparatus by so 

 many careful hydroid observers, e.g., with Nutting in the case of Sertularia pumila, 

 it is evident that the adoption of a system based on such a character instead of bring- 

 ing about a desirable degree of unanimity will tend to make the disagreement much 

 more pronounced. 



There can be little natural about a system of classification that makes it necessary 

 to combine the genera Ahietinaria and Diphasia into a single genus to make it fit in 

 with the classification when the differences are so evident that they are immediately 

 separated into the same two parts but called groups instead of genera for appearance, 

 sake. 



Levinsen objects to certain genera because there are intergrading forms but his 

 classification leaves just as large a crop of these as is to be found in any other system. 

 There will always be these intergrading forms but nothing is to be gained by crying 

 down one system on this account when no improvement is made in a proposed sub- 

 stitute. When an attempt is made to fit in a system of classification of the Sertu- 

 laridae depending on the nature of the opercular apparatus with the general clasisifica- 



