3°4 
THE TANGANYIKA PROBLEM. 
cavity of the first ectodermal invagination of the bud, and 
quite visible from without. This is the rudiment of the 
manubrium of the bud. See Fig. 3. About this time the 
velum becomes perforated in its centre, the four primary 
tentacles stand stiffly out, and each small medusa, although 
still not fully formed and attached to the parental manu- 
brium, pulsates with great vigour. By this time the bud 
has become much constricted off at its base, and as this 
tendency becomes greater the endodermal cavity of the 
manubrial boss breaks through into the cavity of the bell, 
forming the new manubrium, the gastric cavity of the 
parent opening for a short space of time actually on to the 
exterior, through the velum of the bud (Fig. 3). Finally 
the bud becomes completely detached, and at the point of 
separation there arises a rapid thickening of the mesoglia 
which forms the rudiment of the lens characteristic of the 
adult. This rapid thickening gradually pushes the endoderm 
lining the bud’s gastric cavity up into the gastric cavity, 
which becomes continually wider and more and more filled 
up with the growing lens, until the endoderm lining the 
door of the stomach is actually pierced, a small circular 
portion of the lens protruding through the endodermal 
lining into the gastric cavity itself as in Figs. 3 and 5. This 
protrusion rapidly increases, so that eventually the endo- 
derm merely lines the walls of the shallow and widely-open 
manubrial tube and a circular ditch round the bulging lens. 
In buds which have been produced asexually in this manner 
it is found that, even before the above stage has been 
reached, their manubriums are already studded with a new 
generation of buds, which in turn go through the same 
process. 
There is, however, sometimes to be observed, especially 
in the solitary parental forms, an interesting modification of 
