ANATOMY OF LIMNOCNIDA TANGANYICZ#. 281 
have increased in number since the previous stage, and the 
older ones are relatively much longer, so that they hang 
through the velar aperture into the subumbrella cavity. 
The tips of some of the tentacles are already provided with 
cnidoblasts. Also in some of the older tentacles a consider- 
able lumen has made its appearance owing to an axial split in 
the endoderm. The gastro-vascular system is well developed 
in this stage. The circular canal is the first to appear as a 
split in the endoderm at the base of the tentacles, and is soon 
placed in communication with the enteric cavity of the parent 
by the four radial canals which arise one opposite to each of 
the four perradial tentacles. Between the radial canals and all 
round the “ glockenkern”’ the endoderm persists as the endo- 
derm lamella. 
Atavery slightly later period the mesogloea makes its appear- 
ance between the endoderm lamella and the ectoderm of the 
exumbrella, as seen in the horizontal section, fig. 15, m. s. 
An Abnormality in Bud-formation. 
As a rule the Medusa buds are situated on the outer surface 
of the manubrium of the parent, but on two occasions a bud 
with free tentacles was found projecting into the stomach 
cavity. This lusus nature in both instances occurred in a 
region where the buds were more closely packed than usual, 
and, consequently, as there was not sufficient room for the 
buds to develop on the outside of the manubrium, they forced 
their way through the wall of the manubrium and grew into 
the stomach cavity—only in a reversed condition, just as the 
young Tenia head grows into the Cysticercus instead of out- 
side it. 
As a result, the disposition of the cell layers and organs in 
such an abnormal bud is completely reversed. The velum 
develops outside the circlet of tentacles and the subumbrella 
epithelium becomes external, while the exumbrella epithelium 
becomes internal. An examination of fig. 16 will make this 
clear. The endoderm is continuous with the general endoderm 
