THE DEVELOPMENT OF I'HE TEMNOCEPHALE.E. 433 
bounding this layer internally, is not a separate and distinct 
layer, but is merely the innermost stratum of the granular 
layer, and in most preparations is not differentiated at all. 
Externally a. limiting membrane forms a pharyngeal cap- 
sule, separating the muscular mass of the pharynx from the 
surrounding parenchyma. Between the external capsule 
and the internal epithelium, in addition to the elaborate 
system of muscular fibres, there are a number of cells and a 
system of nei’ve-fibres. The cells are of several kinds, com- 
prising bipolar nerve-cells, excretory cells, and unicellular 
glands, the ducts of which are usually said to open into the 
cavity of the pharynx. 
I’osteriorly the pharynx leads through a short passage — 
the oesophagus — into the spacious intestine. Bound the 
oesophagus are a number of unicellular “ salivary ” glands. 
The intestine in all the Australasian species (and also in 
T. chile usis according to Wacke) is constricted at intervals 
by a number of annular muscular dissepiments, the number 
of these varying with the species. The epithelium is com- 
posed of long narrow cells, the majority of which, though 
probably mainly absorptive in function, contain vacuoles 
enclosing granules which are probably excretional, while 
others are of the nature of unicellular digestive glands. 
The pharyngeal sac, the pharynx with the oesophagus, and 
the intestine are all derived from different sources. The 
first may be said to be of the nature of a stomodseum. The 
pharynx is derived from a portion of the wail of the eudo- 
coele. A number of large cells become arranged in a manner 
presenting the appearance of an epithelium on the wall of 
this region, separated from the internal space by the thin 
epithelial liniug of the cavity. This specially modified por- 
tion of the wall then becomes rounded off as the wall of the 
pharynx, what remains of the cavity, which becomes much 
diminished in size, forming a short passage corresponding in 
position with the future oesophagus, and terminating abruptly 
behind in the mass of yolk. 
The large cells in the wall of the embryonic pharynx at 
