PEDAL LACERATION IN ACTINIANS. 95 



of the remaining mesenteries he would homologize with the glan- 

 dular streak (Nesseldriisenstreif) of the trilobed filament. Thus, 

 according to his interpretation, the actinian filament is a double 

 structure. 



H. V. Wilson (loc. tit.'} working on the coral Manitina, where 

 the filament consists of a single lobe, reached the conclusion 

 that this type of filament was comparable to the trilobed actinian 

 filament and is entirely of ectodermic origin. 



McMurrich, 1891, describes a double origin for the trilobed 

 filaments of Rhodactis and Aulactinia; after the manner suggested 

 by E. B. Wilson. 



Duerden, 1899, working on Lebrunia, where the mesenteries 

 become developed before the stomodeum becomes hollowed out, 

 concluded that in this case part, at least, of the filaments are of 

 endodermic origin since he finds stages where filaments are present 

 on some of the mesenteries which as yet have no direct con- 

 nection with the stomodeum. 



Appellof (loc. tit.) concludes that the mesenteric filaments 

 are developed entirely from the ectodermal downgrowth from 

 the lining of the stomodeum. He mentions having observed 

 a number of instances where the ectodermal layer had become 

 very much attenuated just below the level of the stomodeum, and 

 indeed in some instances the continuity of this layer had been 

 broken. He argues from this fact that some of the instances 

 observed by previous workers who, on the basis of a lack of con- 

 tinuity between the mesenteric filament and the lining of the 

 stomodeum, maintained the endodermic origin of the filaments 

 might be simply cases where the continuity of the tissue had been 

 broken and in no way fundamentally different from the ordinary 

 course of events as he has described them. He also makes the 

 suggestion that the method of development described by E. B. 

 Wilson for the alcyonarian filaments may be confined to those 

 individuals which arise as buds and not a true explanation of what 

 takes place during embryonic development, which he tacitly 

 assumes would be similar to plans followed in other Anthozoan 

 forms. 



In all descriptions of the formation of the mesenteries, and 

 particularly of the mesenteric filaments, except that of Duerden 



