270 
J. STEPHENSON. 
allow of much being seen in dissection, but examined micro- 
scopically it presents a number of interesting features which 
go some distance towards elucidating the origin of the cells. 
The Disposition of the Cell-masses in H. cali- 
ginosus (PL 19, fig. 6). — The combined mass of chromophil 
cells is situated dorsally on the pharynx, and extends back- 
wards as far as septum 5/6. The cellular aggregate appears as 
a number of white lobes amongst the muscular strands ; the 
general arrangement is one of four transverse bands. The 
posterior of these transverse elevations is divided into two 
by a cleft in the mid-dorsal line, and forms a single rounded 
pillow-like mass on each side (c 4 ). The next is not divided, 
and forms a single transverse elevation across the dorsum of 
the pharynx (c 3 ). The second is divided up into a number of 
separate lobules, (c 2 ), and appears therefore as a transverse 
row of rounded projections. The first is similar to the 
second (c 1 ). 
The cellular masses extend downwards on the sides of the 
pharynx about as far as the lateral line or a little further ; 
the first transverse row may be shorter. 
Each lobule of the two anterior rows is associated with a 
muscular strand (m), the base of which it surrounds. The 
third, undivided elevation, has a number of muscular bands 
emerging in a transverse series from its posterior face. The 
fourth is not associated with muscular strands. 
The General Relations of the Cell-masses in H. 
parvus (PI. 19, fig. 7). — As seen in sections, the much 
lobulated pharyngeal cell-mass (c 1 , c 2 , c 3 ), situated dorsal to 
the pharynx, extends also behind this region, and partially 
surrounds the first part of the oesophagus. It thus occupies 
segments IY, Y, and YI ; the portion in segment YI is to 
some extent separate, being divided from the rest by septum 
5/6, through which it communicates with the anterior portion 
by a constricted neck. In segments IV and Y the mass is 
penetrated by a number of muscular strands. 
But in this species the characteristic cells have a con- 
siderably greater extent of distribution than in the forms 
