362 CHARLES L. BOULENGER. 
whorl of three large barbs and two or three distal whorls of 
much smaller ones. 
(2) A smaller barbed form, similar in all respects to that 
just described, but attaining only half the size. It is found 
in the same positions as the larger kind. 
(3) A cylindrical nematocyst of slightly greater length but 
same diameter as (1), without barbs. ‘The thread before 
eversion is coiled round the imaginary longitudinal axis, 
forming several coils (fig. 9, c). This form differs from the 
corresponding nematocyst of Hydra in the character of the 
thread, which is thicker; the coils, moreover, are further 
apart and fewer in number. ‘This nematocyst is rare, and I 
have only come across a few examples in the tentacles. 
(4) A small pip-shaped form, devoid of barbs, occurring in 
large numbers, chiefly in the tentacles. The thread is thick 
and short; it differs from that of the cylindrical nematocyst 
in being coiled round the transverse axis of the organ 
(ho O dpe 
B. Medusa-buds. 
On the larger hydranths medusa-buds are to be found 
scattered about the broadest part of the body, between and 
below the bases of the tentacles (fig. 6, 7, Med.). They arise’ 
in the usual manner as hollow outgrowths of the wall of the 
gastric cavity. ‘heir development seems quite typical; the 
future umbrella cavity makes its appearance in the ectoderm 
at the apex of the bud, and by its growth causes the 
approximation of the endodermal walls of the latter. ‘This 
leads to the formation of the endoderm lamella and the radial 
canals. Manubrium, velum, and other organs arise in the 
usual way. During the later stages of its development the 
medusa is borne on a short slender stalk. 
The four-rayed symmetry so characteristic of the adult can 
be made out early, and the rudiments of the tentacle-bulbs 
are large and conspicuous. The tentacles themselves do not 
seem to be formed until after the liberation of the medusa. 
