84 
ANNIE MATTHEWS. 
part is absorptive. Food is engulfed by the amoeboid processes 
of the latter cells in common with the endoderm cells lining 
the general body cavity (12). The above observations 
probably explain why in Miss Pratt’s paper ((12) PI. 21, 
fig. 4) the carmined food is absorbed, and has reddened the 
filament in certain definite areas and not in others. The 
colourless parts are the ectodermic and the reddened parts 
the en do dermic areas twisted uppermost. It also explains 
the observation made early in the same paper, that histo- 
logical study of the “stomodEemn and ventral mesenterial 
filaments in several members of the family reveals many 
points of similarity, if not identity, in their elemental consti- 
tution. Both granular and mucous gland cells, as well as 
nematocysts, occur in all these structures.” Briefly, this is 
because the secretory part of these filaments is ectodermic, 
the requisite gland cells and nematocysts being supplied by 
the downgrowth from the stomodseum. The dorsal filaments 
are very much narrower and straighter than the ventral in 
the solitary polyp. A transverse section of these dorsal 
filaments two days after they first appear is only two-tliirds 
the size of a similar section of the ventral filaments on 
the same date. No indication of these dorsal filaments is 
found until the sixth day, i.e. they arise later than the 
others. Narrow processes of the stomodseal ectoderm are 
then seen growing down over the uppermost part of the 
free edge of the two dorsal mesenteries, thus giving rise 
to the filaments (PL 4, fig. 26, D. 0.). No appreciable 
thickening of the endoderm forms, however, as a support 
for this ectoderm, whereas it was visible before the ecto- 
dermic part in the ventral filaments. A transverse section 
reveals that in rough outline the dorsal filament is quite 
comparable to the ventral, the difference being one of 
degree of development only (Text-figs. 49 and 51). In the 
former the ectodermic band, consisting of tall ciliate cells 
with deep staining nuclei, rests on a slender endodermic 
support, which is smaller than in the ventral filament. 
Therefore both kinds of filament consist of ectodermic and 
