98 PROCEEDINGS OF THE ACADEMY OF [Feb., 



ways : that from the ventro-mediau group passes into the central 

 ciliated chamber (m.c.h.) and thence directly out through the duct 

 (v. e.g.), while the secretion from the dorso-lateral group has to 

 pass into the duct through the side pouch (p.). Anterior to the 

 duct, the ciliated chambers (m.c.h. and l.c.h.) being one (fig. 5/, 

 m.c.h.), the secretion from the different groups of cells may, of 

 course, pass out either way. The duct is inclined, somewhat, in a 

 postero-ventral direction and is lined Avith ciliated columnar cells. 

 The point at the end of the line 1 (fig. 5i) indicates the place of 

 union of the medial part (fig. 5/i, 1. ) of the ciliated layer with the 

 adjacent side (1'.) of the deep ciliated groove (v. e.g.). Reference 

 line 2 shows where the lateral part (2) of the cover layer joined 

 the outer side (2') of the ciliated pouch (p.). Reference line 3 

 indicates the point at which the lateral part (3) of the ciliated 

 layer joined the medial side (3') of the ciliated pouch (p.). m.l. 

 is the median lamella formed by the union of the medial portions 

 of the cover layers (d.l.) of the two parts of the gland; from this 

 point it is an incomplete partition all the way to the posterior end 

 of the gland. 



Posterior to the duct (fig. 5/), the medial portion (1.) of the 

 ciliated layer joins .its fellow of the opposite side, above the median 

 lamella (m.l.), while the outer part (3) of this layer remains con- 

 tinuous with the outer part of the cover layer. By this arrange- 

 ment the lateral invagination (i.v.) apparently completely separates 

 a lateral from the central part of the gland, as has been mentioned 

 before, and the mesoblast cells are found between the two divisions 

 (mes. ). This is shown also in fig. om, which is a horizontal section 

 of the entire gland. A section at this plane gives the impression 

 that the lateral invagination (i.v.) almost completely separates the 

 lateral from the central portion of the gland, but of course if the 

 section were cut nearer to the dorsal surface of the gland, the 

 lateral portion would be seen to be joined to the central portion 

 anterior to the duct (to the left of m.l.), as has been seen in figs. 

 ^ye-h. Fig. 5m shows the extent to which the gland is completely 

 divided by the partition (vi.l.), and also the position of the gland 

 in relation to the gill-arches (v. a. , 2-5), The cilia are omitted from 

 this figure. In all the sections posterior to the duct, as seen in fig. 

 5/, there are three distinct ciliated chambers. The median ciliated 

 chamber (m.c.h.), occupying the central division of the gland, is 



