no GEORGE MATTHAI 



and larger at the insertions of mesenteries. These processes are 

 composed of fibres and cementing substance, and are the 

 homologues, in the column- wall, of the pleats in mesenteries 

 and tentacles. 



The superficial longitudinal fibres in the pleats of mesenteries 

 and tentacles are specially thickened. These specialized fibres, 

 which vary in thickness, appear to be composed of fibrils, 

 but had usually been supposed to be similar to the muscular 

 elements described by the Hertwigs in Actinians, Faurot in 

 1895 being the first to doubt their muscular nature. In teased 

 preparations and in sections, nuclei are not found in these 

 fibres nor is there any morphological or physiological evidence 

 for regarding them as muscular. Speaialized fibres are present 

 on the exocoelic side of mesenteries (but not so thick nor so 

 close together as on the entocoelic side), although pleats are 

 absent from that side or only a few feebly developed ones 

 are present near the stomodaeal attachment. The striae in 

 the processes of attachment appear to be specialized fibres which 

 have a radial disposition. 



In preparations of mesenteries with the endodermal lining 

 scraped off, the specialized longitudinal fibres of the middle 

 lamina could be seen running along its entire length. When 

 parts of the living tissue of Isophyllia were isolated from 

 expanded colonies, teased in sea-water, and stained in methy- 

 lene blue, the middle lamina took a purple or violet tinge 

 and its fibrous texture became quite apparent. The fibrous 

 condition could also be unmistakably seen in properly pre- 

 served tissue which had been teased after maceration and 

 removal of the protoplasmic sheets, as well as in such tissue 

 cut to 4 M and 6 ij- thicknesses. The branching fibres were 

 best seen by staining in safranin and picro-nigrosin. The 

 specialized fibres of the middle lamina, whether in the pleats 

 or in the processes of attachment, were similarly coloured wdth 

 different stains, e.g. dark in iron haematoxylin, purple in 

 aniline blue and orange G, slaty blue in borax- carmine followed 

 by picro-nigrosin, such results suggesting identity of texture 

 of both sets of fibres. The absence of muscular fibres in the 



