510 G. HERBERT FOWLER. 
epithelium of the adult. These two masses of ectoderm no 
doubt represent the “ Glockenkern” or entocodon, ‘“ that im- 
portant organ by means of which the cecal bud becomes trans- 
formed into the medusa, the growth of ectoderm at the tip of 
the bud, already noted and described by so many authors under 
various names, which presses on the endoderm tube, and thus 
produces a hollow goblet-shaped reduplication of endoderm, 
from which proceed the endodermal structures of the medusan 
bell” (Weismann, ‘ Entsteh. Sexualzellen Hydromed.,’ p. 16). 
In the endoderm the radial canals, the core of the manubrium 
and its cavity (esophagus) are already differentiated. At the 
present apex of the medusoid is a slight depression, the edges 
of which are thrown into short conical processes, consisting of 
ectoderm with a solid endodermal core ; these may represent 
either the folded edges of the velum, or more probably, since 
in the youngest free medusoids observed by Lankester the 
velum was not distinguished, the rudiments of the future ten- 
tacles ; there are about eight of them. On each side of the 
cesophagus is a small blind tube in the substance of the manu- 
brial endoderm, which was apparently natural. The mesoglea 
lamina was indistinguishable. 
With the certain knowledge that the medusoid is the product 
of a hydroid, the possible alternatives which the life-history of 
Limnocodium may present are reduced to three!: either (1), 
as Brooks suggests (‘ Mem. Boston Soc. Nat. Hist.,’ iii, p. 385), 
the present stock is due to the introduction into the tank of 
hydroid individuals capable of budding only male medusoids, a 
process repeated year by year; or (2) female medusoids are 
formed on the hydroid stocks, but are never freed; or (8) 
Limnocodium may be an instance of some such reproductive 
method as the “sporogony” described by Metschnikoff in 
certain Cunine (‘ Embryologische Studien an Medusen’). In 
1 So many hundreds of medusoids have been examined at all times of the 
year, that it is most improbable that the existence of free females should 
have escaped notice. 
