366 CHARLES L. BOULENGER. 
approaches maturity the jelly or mesogloea increases in thick- 
ness, especially in the apical region where it may attain a 
depth equal to nearly one half the total height of the medusa. 
The ex-umbrellar surface is perfectly smooth and devoid of 
groups of thread-cells. 
The velumis broad and muscular, and is a very conspicuous 
feature of the jelly-fish. 
The digestive sac or manubrium varies in shape according 
to age; it is, however, always short, and even when fully 
extended never reaches much further than the middle of the 
umbrella cavity. 
The mouth is approximately circular and is simple, being 
devoid of oral lappets or appendages such as occur in so 
many families of Anthomedusz. 
Sections of the distal portion of the manubrium show this 
organ to be approximately cylindrical in shape. 
The endoderm is seen to form four very conspicuous ridges, 
inter-radially situated, extending along the whole length of 
the manubrium as far as the base of the stomach proper. In 
the oral region the individual cells are tall and narrow with 
abundant finely-granular protoplasm, and a basally situated 
nucleus. 
These cells pass gradually into a second kind of endoderm- 
cell which lines the cavity of the central region of the manu-— 
brium; in these the nucleus occupies a central position, and 
divides the cell into a basal portion with clear protoplasm and 
a peripheral portion with finely granular contents which stain 
deeply. Wedged in between. these cells are occasional club- 
shaped gland-cells with large nuclei and coarsely granular 
protoplasm. 
In the stomach or proximal region of the digestive sac the 
inter-radial ridges are less conspicuous, and the endoderm 
lower ; the cells are much vacuolated, and many are modified 
as plane -cells. 
In a medusa which has not long been liberated ane proxi- 
mal region is seen to be considerably swollen. 
_ The swelling becomes accentuated in slightly older speci- 
