No. 6.] THE MORPHOLOGY OF THE ACTINOZOA. 253 



be stated that their participation in the digestive processes 

 seems to be now generally accepted, chiefly owing to the 

 observations of Krukenberg (80), and Metschnil<off fso), and, 

 more recently, of VVillem ('93). 



The earliest recognition of a difference in the structure o 

 the upper and lower portions of the filaments was by Bollard 

 (.51) who, however, merely noted its existence. A more care- 

 ful description of the upper part of the filament was given by 

 Haime C54), who not only recognized the acontia and the glan- 

 dular streaks, but speaks of the upper part as " gros cordons, 

 each of which has attached to its sides " un feston tres regulier 

 et muni de cils puissants." Thorell fss) also recognized the 

 same three portions, terming the acontia "capsule cords the 

 glandular streaks " mesenterial threads," and the ciliated bands, 

 on account of their proximity to the reproductive organs, "ovary 



'°R'athke, in .840, had observed that the acontia of iktridUm, 

 d,anthus(Aa. plumosa) were solid structures and not hollow, as 

 had usually been supposed; and, a year later, Leuckart (4i) 

 advanced the idea that the mesenterial filaments were also 

 solid Some later authors, such as Haime and Thorell, adhered 

 to the earlier ideas ; but Gosse feo) described them as cords and 

 named them craspeda, failing, however, to recognize the chated 



''''The first careful study of the filaments by modern methods 

 was made by von Heider C77). He confirmed Leuckart s obser- 

 Tt ons as to their solidity, showing that the central axis of the 

 fiCnt was really the expanded edge of the connective Ussue 

 (mesogloea) of the mesentery. He also figured the trilobed 

 1 Utton of the upper part of the filament, but failed o per- 

 ceive the peculiar nature of the epithelium of the lateral lobes, 

 ah of which according to his idea "das fur die Mesentena - 

 filamente charakteristische Epithel trug." .^H--^,-^- ; 

 to have regarded the lobes merely as coils of the glandular 

 Dortions of the filaments. 



Finally, in .879. the brothers Hertwig gave a very thorough 



account o the structure of the hexactinian filaments, and prac- 



caly nothing has been since added to our knowledge of them. 



