30 Report on the pennatulida. 



numerous spherical nucleated cells occur : these are always in close 

 contact with the eudoderm cells, but whether they properly belong to 

 the endoderin or not we have been unable to determine. They may 

 perhaps be described as mucus cells. 



The pinnules have the same structure as the tentacles. Each 

 is hollow, its cavity opening into that of the tentacle (Figs. 

 10 and 11), and. its wall consisting of ectoderm, mesoderm, and 

 eudoderm, having the same structure and proportions as in the 

 tentacles, differing only in being of less thickness. 



d. The Stomach. — The mouth is not circular, but, as in the majority 

 of Actinozoa* a transverse slit. The section drawn in Fig. 12, though 

 taken a short distance below the mouth, shows thischaracter very well. 

 The direction of the axis of the moiith, which is a constant one, we 

 shall refer to after considering the arrangement of the mesenteries. 



The mouth leads by a short oesophagus into the stomach (Fig. 10 n), 

 the walls of which are thrown into transverse folds, as shown in the 

 figure : these folds become much more marked when the tentacles are 

 retracted, the whole stomach being then shortened by the approxima- 

 tion of the folds, somewhat after the manner of a concertina, and thus 

 providing space within the calyx in which the retracted tentacles are 

 lodged. At its lower end the stomach opens into the body cavity by a 

 slit-like orifice, the direction of which corresponds to that of the 

 mouth. 



The stomach-wall consists (Fig. 10) of (1) an inner lining membrane 

 which at the margin of the mouth becomes continuous with the 

 external ectoderm, and is therefore described as ectoderm ; (2) of a thin 

 mesoderm ; and (3) of an outer layer or eudoderm continuous with that 

 of the tentacles and of the body-wall. 



The ectoderm (Figs. 10 and 13, ic) is a thick layer, consistmg of 

 much elongated columnar ciliated cells, between which are other 

 elongated cells with a very granular appearance, and probably of a 

 glandular nature : at the inner or free surface are seen at intervals 

 what appear at first sight to be clear spaces, but which are almost 

 certainly cells similar to those described in Anemones by the Hertwigs 

 as mucous cells, f The deepest or outermost part of the ectoderm 

 contains fusiform and spherical cells imbedded between the bases of 

 the longer ciliated and glandular cells. 



The mesoderm of the stomach (Figs. 10 and 13, .r) is a very thin 

 fibrillated layer of connective tissue, in which we have not detected any 

 definite muscular bands. We have found no traces of sphincter 

 muscles round either the mouth or the lower aperture of the stomach. 



The endoderm (Figs. 10 and 13 y) is chiefly characterised by 

 containing an enormous number of extremely minute and highly 



♦ Vide Gosse ; Heider, etc., op. cit. 



I O. und K. Hertwig: Op. cit., pp. 58-60, and Taf. III., Fig. 6, where the two 

 kinds of gland-cells, viz., gi-anular and mucous, are described and fiRured, 



