LIFE-HISTORY OF MELICERTIDIUM 343 
manubrium short, showing four blunt, radially-placed, crooved 
angles. At first the bell shows a small pit in the middle of the 
aboral surface, to the bottom of which a cone-like projection 
of the stomach is anchored. Later this remnant of the con- 
nexion between bud and stalk becomes severed, and the summit 
of the dome shows an upward convexity (fig. 17). Over the rest 
of the bell, the mesogloea superficial to the plane of the stomach 
and radial canals forms a relatively thin layer. At their bases 
the tentacles are hollow and slightly swollen, the endoderm 
here containing yellowish intracellular pigment. The measure- 
ments of the young medusa at rest are: height 1-2 mm., 
breadth 1-3 mm., interradial diameter of stomach 0-45 mm. : 
breadth of radial canal 0-06 mm., depth of superficial meso- 
gloea 0-075 mm. The surface of the bell shows numerous 
minute glancing-points which do not disappear on treatment 
with acid. ‘lhe medusae were kept alive for a time, and increased 
in size; the four interradial tentacles grew almost as biz as 
the radial ones, and new tentacle buds appeared in irregular 
sequence, one for each interspace between a radial and an 
interradial tentacle. Stages with ten, twelve, fourteen, and 
sixteen tentacles were thus obtained. Medusae four weeks old 
and with c. ten tentacles showed a single blunt outgrowth 
from the stomach in each interradius (fig. 18, b). A week later 
(cv. twelve tentacles) these outgrowths had extended over the 
sumuut of the bell, becoming pointed at their ends. In another 
week or fortnight (c. fourteen to sixteen tentacles) the out- 
growths had extended downwards along the sides of the bell 
and become continuous with slender corresponding upgrowths 
from the ring canal (fig. 19). I failed to rear the medusae 
further, but they had already reached the eight-rayed condition 
characteristic of Melicertidium. 
I have not obtained the early four-rayed medusae in tow- 
nettings off the Millport Station, but they were moderately 
abundant during April 1919 in plankton from the Gareloch,! 
an inlet farther up the Firth of Clyde. 
Since this paper was written, I have found the intermediate stages 
described above in May plankton from this locality, and the adults 
at the end of June. 
