BY JAS. P. HILL. 
11 
heart bladder to form the proboscis canal which opens on the 
right side. 
With regard to the behaviour of the dorsal proboscis pockets, 
Pt. qu&traliensis appears to be the most variable of all the 
Enteropneusts hitherto described. 
No to chord (Eichel-darm of Spengel) : In shape the notochord 
of this species essentially resembles that of Pt. minuta. Imme- 
diately anterior to the point of opening of the lumen of the 
notochord into the mouth or throat cavity, its narrow neck portion 
is dorso-ventrally compressed, with a convex dorsal wall and a 
concave thin ventral wall composed of a single layer of low 
columnar cells resting on the proboscis skeleton (fig. 16, div.). 
Anteriorly in the region of the proboscis neck the neck portion of 
the notochord is not so much dorso-ventrally compressed, but 
somewhat higher and with a more or less triangular lumen. The 
dorsal wall of the neck portion of the notochord is very much 
thicker than the ventral and is composed of long narrow epithelial 
cells which radiate outwards from the lumen and have central 
generally narrow rod-like nuclei. Between these elongated cells 
there occur numerous clear oval bladders which Spengel well 
regards as the secretory holders of gland cells. Some appear quite 
empty, others again show a network in their interior similar to 
that in the epidermal mucous glands and which stains in the same 
diffuse manner. They thus conform, as Spengel has shown, to the 
structure of the "goblet cells;" on the ventral side where the wall 
is composed of a single layer of columnar cells, these gland cells 
are entirely absent. The neck portion of the notochord is thus 
distinctly epithelial in character. 
Anteriorly the dorsal wall increases considerably in thickness, 
while the cells of the ventral wall lose their distinctly columnar 
quality. They become longer and narrower, gland cells appear 
between them, and they finally pass over into the chorda-like 
tissue forming the wall of the ventral blind sac of the notochord. 
The lumen of the notochord extends obliquely downwards into 
the ventral blind sac (fig. 14), then in this the lumen extends 
