THE TANGANYIKA PROBLEM. 
3°3 
small knobs, these knobs being, in reality, the initial rudi- 
ments of future medusoid buds. As the season advances 
such rudiments go through a rapid metamorphosis, they 
become definite hollow evaginations leading from the gas- 
tric cavity. The little pouches thus formed thicken at their 
apices, and an invagination of the ectoderm of the manu- 
brium takes place at these points, each invagination becom- 
ing cut off from the exterior. The ectodermal lining of 
tig- 3- Semi-diagramatic representation of the formation of asexual buds of the 
Tanganyika medusa. The thick black line is the endoderm. 
these cavities becomes the ectoderm of the interior of the 
bell and the manubrium of the growing bud, as well as 
forming the inner surface of the imperforate velum. Still 
later a second, shallower invagination takes place, forming the 
mouth of the bell, and within this the four primary tentacles 
are at first folded inward towards the centre of the velum. 
About this time the endodermal lining of the parental 
manubrium (which projects into the bud from its gastric 
cavity and forks into four radial canals) becomes thickened 
and folded, so as to form a rounded boss projecting into the 
