STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 
293 
my conviction that in the “dorsal organ ” of the Entoprocta 
we may recognise the supr a-oesophageal ganglion or 
brain of these animals. 
The horizontal 1 section fig. 43 cuts the oesophagus (ce.) 
and the intestine ( int .) ; the epiblast is somewhat thick, as 
this is the region of the ciliated ring. The space between the 
alimentary canal and the epiblast has increased in size ; on the 
right side is a mass of mesoblast cells growing forward from 
the region of the anus, the left wing of the mesoblast not being 
seen, owing to a slight obliquity of the section. Between the 
oesophagus and the intestine occurs a bilobed, apparently solid, 
mass of cells which are derived from the epiblast, and repre- 
sent an early stage in the development of the vestibule. Each 
of the halves of the bilobed mass in reality corresponds to a 
shallow depression of the ventral surface of the embryo in 
front of the anus. 
Fig. 41 represents a section of a somewhat later stage, 
passing in an obliquely longitudinal direction and cutting one 
side of the oesophagus (which is considerably elongated trans- 
versely), and also a vestibular invagination. Behind the latter 
occurs the commencement of one of the paired mesoblastic 
bands, which is seen passing forwards and breaking up into an 
irregular mass of branching mesoblast-cells. Anteriorly is 
cut one of the two lateral halves of the brain, which has 
already grown inwards as a pair of wings, one on each side of 
the oesophagus. In a horizontal section of a considerably older 
stage (fig. 44), each vestibular invagination is composed of 
cells, whose nuclei are arranged in several layers. The section 
shows anteriorly a portion of the ciliated ring, indicated by the 
thickness of the epiblast and the elongation of the nuclei, 8 
1 This term is used somewhat loosely in the description; in some “hori- 
zontal ” sections, for instance, the oesophagus and stomach are cut ; in others 
the oesophagus and intestine or rectum. 
2 The existence of the nuclei on the outer side of the cells of the ciliated 
ring in the figure is due to the fact that a slight fold of the body wall has 
been produced by the action of reagents, and has been involved by the 
section ; the cells of the ciliated ring are of course part of the external 
epiblast. 
