MATTHAI— RECENT COLONIAL ASTR^ID^ 27 



" mesenterial lobes" by H. V. Wilson, which he regarded "merely as a device to support 

 the filament " (p. 225). 



A short distance below the stomodasum, the margin of each primary mesentery is 

 drawn out into long ribbon-shaped prolongations which, with the filament continued along 

 their free edges, lie coiled together in the gastro-vascular spaces. The free margins of 

 mesenteries which do not meet the stomodeeum are also drawn out into such processes. 

 When these processes are cut across they appear as bars of mesenterial tissue, usually 

 curved, with the filament on either side of each bar (PL 3, fig. 30). They are also found 

 extended into the inter-mesenteric spaces of the edge-zone but, as a rule, are scarce in the 

 region above the enterostome, while below it they may be massed together in the gastro- 

 vascular chambers. These convolutions are often found in the peristome, protruded 

 through pores (? artefacts) in its fioor (this observation is based on the preserved material) ; 

 they may also be ejected through the mouth, but this is less frequently the case as 

 in sections I have noticed them in the stomodsea of only Echinopora and Favia ananas 

 (Ell. and Sol.). 



Mesenterial filaments (PI. 1, fig. 6 and PL 3, fig. 30). Every mesentery which 

 meets the stomodseum and most of the others bears a filament (the " craspedum " of Gosse 

 and " enteroide" of Faurot) on the free margin of its straight region and along the entire 

 edge of the coiled ribbon-shaped processes into which the mesenterial margin is prolonged. 

 The filament terminates a short distance from the insertion of the mesentery to the basal 

 disc. The structure of the filament can be best made out in a primary mesentery. It 

 consists of a median part and two lateral extensions (the " main body " and the two 

 " ventro-lateral tracts " of H. V. Wilson), the former is the continuation of an ectodermal 

 ridge of the stomodseum, while the latter arise from the stomodseal ectoderm on each side 

 of the ridge. The lateral extensions lie like two flaps over the mesenterial endoderm to 

 a short distance below the stomodseum (PL 1, fig. 5). The stomodseal ectoderm is also 

 reflected upwards to some distance, this being continuous with the downward lateral 

 extensions referred to. In the region of this upward reflection, the stomodseal endoderm 

 comes to lie between two layers of ectoderm. 



The mesoglsea of the stomodseal wall, however, is continued upwards and downwards 

 along with the ectoderm, separating the latter everywhere from the endoderm. The 

 lateral extensions are soon tucked inwards and come to lie behind the median tract. The 

 mesoglsea in the filament then appears T-shaped in transverse section, the handle of the T 

 is the termination of the mesenterial mesoglsea, while the two arms are due to the 

 downward extensions of the stomodseal mesoglsea. The so-called forking of the margin of 

 the mesoglsea is therefore not a case of bifurcation at all. In the earlier sections the 

 filament appears somewhat triangular while, lower down the straight region, it becomes 

 more consolidated and appears hemispherical or almost circular in transverse section. The 

 straight region of the filament is ciliated. The nuclei of the filament are of the same 

 nature as in the stomodseal ectoderm, massed together concentric to the periphery of 

 the filament, incomplete at its base where the mesoglsea enters the filament. In the 

 median part of the filament granular vacuoles are usually present, their granules varying 

 in size. 



