1898-99. | THE MESENTERIAL FILAMENTS IN ZOANTHUS SOCIATUS. 389 
mesenterial filaments were also solid. Some later authors, such as 
Haime and Thorell, adhered to the earlier ideas, but Gosse (1860) 
described them as cords, and named them craspeda, failing, however, to 
recognize the ciliated bands. 
The first careful study of the filaments by modern methods was made 
by von Heider (1877). He confirmed Leuckart’s observations as to their 
solidity, showing that the central axis of the filament was really the 
expanded edge of the connective tissue (mesoglcea) of the mesentery. 
He also figured the trilobed condition of the upper part of the filament, 
but failed to perceive the peculiar nature of the epithelium of the lateral 
lobes, each of which, according to his idea “das fiir die Mesenterial- 
filamente charakteristische Epithel trug.” He seems, indeed, to have 
regarded the lobes merely as coils of the glandular portion of the 
filaments. 
Finally, in 1879, the brothers Hertwig gave a very thorough account 
of the structure. of the Hexactinian filaments, and practically nothing 
has since been added to our knowledge of them. The Hertwigs showed 
that they are solid structures, and that two portions are recognizable 
(three in the Sagartiade, which possess acontia). The upper portion 
consists of two wing-like lamellae attached to the edge of the mesentery, 
which, in consequence, presented a somewhat trilobed condition in 
transverse section. The two lateral lobes are characterized by the 
epithelium of their outer surfaces being composed of long and very 
narrow cells, each of which bears a single cilium. These cells vary 
somewhat in length at regular intervals, so that longitudinal sections 
show the lobes to have a wavy contour. No glandular or nematocyst 
cells occur in this portion of the filaments which the Hertwigs termed 
the Flimmerstrezyf. 
The lower portion consists of a more or less coiled cylindrical cord 
attached throughout its entire length to the edge of the mesentery. Its 
epithelium consists of gland cells, nematoblasts, supporting cells (Stiitz- 
zellen), and sensory cells, the nerve fibres from these last forming a 
plexus between the bases of the other cells. This portion was termed the 
Nesseldriisenstreyf,. \n its upper part it is an almost straight cord, and 
in perfect mesenteries is continuous with the central lobe of the cili- 
ated bands, and through this with the stomatodzal ectoderm ; in imper- 
fect mesenteries, however, there is no such continuity with the ectoderm, 
the glandular streaks gradually fading out above, and the central lobe 
of the ciliated bands being wanting, the lateral lobes are separated by a 
depression lined by ordinary endoderm cells. It would seem from this 
