200 J. H. ASHWOETH. 



In teased preparations the muscle-fibres of the ordinary endoderm 

 cells may be clearly seen (Fig. 26). On looking at the flagella-bearing 

 cells in the same preparations, it is seen that most of these colls bear 

 at their inner ends two processes which appear to be less stiff than the 

 muscle-fibres of the ordinary endoderm cells, and which are never in a 

 straight line with each other, but are invariably bent more or less 

 towards each other (Fig. 27). It is possible that these are the modified 

 muscle-fibres of the cell, as they appear to be homogeneous, and, when 

 treated with fuchsin or iron hsematoxylin, stain similarly to, though 

 rather less deeply than, the muscle processes of ordinary endoderm 

 cells. The bending inwards of the two processes from the inner end of 

 the cell causes them to become rather more deeply embedded in the 

 mesogloea than the muscle processes of the ordinary endoderm cells, 

 and the cell is therefore provided with a firmly fixed base upon which 

 the giant flagellum can work as on a fulcrum. 



It is worthy of note that throughout the whole of the colony the 

 muscle processes of the endoderm cells (except the protractor and 

 retractor muscles on the mesenteries) are circular in direction, whereas 

 the similar processes (where present) of the ectoderm cells are longi- 

 tudinal in direction. 



Zooxanthellse are exceedingly numerous in the endoderm of the 

 pinnules, so numerous that, in many cases, the lumina of the pinnules 

 are entirely closed. They are also numerous in the endoderm of the 

 tentacles and of the free portion of the polyp, but in the ccelentera of 

 the stem there are few, except near the upper end. There do not 

 appear to be any large gaps between the endoderm cells in the lower 

 parts of the ccelentera, as described by Hickson in Alcyonium, but the 

 endoderm cells in this part are more or less spherical in shape, and are 

 only loosely connected together. 



Mbsoglcea. 



1. Of the Free Portion of the Polyp. — The mesogloea of the body of 

 the polyp varies in thickness from "02 mm. to 06 mm., while that of 

 the tentacles is much thinner, averaging *013 mm. The mesogloea of 

 the pinnules is exceedingly thin, especially when they are expanded (cf. 

 Figs. 11, 17). 



Cells which connect the ectoderm and endoderm may be seen cross- 



