224 WILSON. [Vot. II. 
the filament in Fig. 52 contains a large number of granular 
gland cells and numerous nettle cells. The mesenteric lobes 
are composed of cells which do not differ essentially from the 
rest of the endoderm; they are only much elongated and con- 
tain a number of very large vacuoles. The passage of the fila- 
ment into the cesophageal epithelium is effected in the following 
manner. Immediately below the cesophagus, the “ waist” in 
Fig. 52 becomes gradually wider until the ventro-lateral tracts 
no longer exist, and the filament cells are continuous with the 
mesentery cells round the horns, 4, of the supporting lamella of 
the filament. At this level, the filament or cesophageal lobe is 
much flatter and wider than it is below (Fig. 52), and the sup- 
porting lamella of the filament is also nearly flat. The latter 
passes directly into the supporting lamella of the cesophagus, 
and the filament into the lining epithelium of the cesophagus. 
Fig. 53 is through the middle third of the filament. The 
gland cells are absent in this region, but the nettle cells are 
very large and exceedingly abundant. The mesenterial lobes 
are not so well developed as in the region above.. 
The lower third of the filament, Fig. 54, contains neither 
nettle cells nor the typical gland cells. The body of the fila- 
ment is here made up of very large granular cells, between 
which are scattered a few supporting cells. The granules are 
much more numerous in the peripheral than in the central halves 
of the large cells, and at the sides of the filament where the 
main body passes into the ventro-lateral tracts, they become 
gradually restricted to the peripheral ends of the cells. The 
granules are chemically different from those in the ordinary 
granular gland cell: they do not stain especially well with heze- 
matoxylin, but become dark brown with osmic acid. In a 
number of filaments these peculiar granular cells contained 
large, irregular concretions, which stained dark red with 
borax carmine, while the cell body stained but faintly. The 
mesenteric lobes in this region are slightly less pronounced 
than in the rest of the filament. In a transverse section through 
the filament of Sagartia, Von Heider (10) has figured the lat- 
eral parts of the simple filament (according to the Hertwigs, the 
section is through the acontium) as composed of just such large 
granular cells as I have described. The Hertwigs do not speak 
of these tracts. 
