178 M. C. Mereschkowsky on a Mode of 
to seven tentacles and with a red ocellus. The manubrium, 
which is deep red, has, when looked at from above, the form 
of a cross (fig. 2, a), from each of the four ends of which starts 
a radiating canal (fig. 2 ,b). Round the mouth there is a 
circle of four tentacles dividing dichotomously into a great 
number of branches. The most remarkable thing about this 
Medusa is that the ova are developed immediately on the sur¬ 
face of the manubrium ; so that the latter, when the ova have 
become converted into planulse, acquires a tuberculate aspect, 
caused by a great quantity of planulse, forming a layer cover¬ 
ing its surface, with one of their ends projecting freely, and 
the other attached to the wall of the manubrium. 
Among the innumerable individuals of this Medusa one 
occasionally meets with some which, at the first glance, attract 
the attention of the observer by the complete absence of the 
coloured manubrium. These are scarcely perceptible, in con¬ 
sequence of their perfect transparency, while ordinarily it is 
easy to follow their movements by the dark red colour of the 
manubrium. I thought at first that I had to do with a per¬ 
fectly different species of Medusa; but on examining it more 
minutely under the microscope I convinced myself that I 
really had before me Bougainvillea paradoxa. 
In fact the form of the bell (PI. XX. fig. 3), the four radial 
canals, the four bundles of tentacles, and the four red ocelli 
are all identical with those of the Medusa that I have just 
described; but what I ascertained, to my great surprise, was 
the total absence of the manubrium. I thought at first that 
there might be a more or less complete atrophy of this organ ; 
and I sought for some remains of it, but in vain. On the 
contrary, I convinced myself that the individuals in question 
were completely destitute of manubrium, and that the whole 
gastrovascular system consisted only of a circular canal and of 
the four radial canals, which were united at the summit 
without forming any thing resembling a stomach (figs. 3 
and 4). 
Moreover I ascertained beyond all doubt that all this gas¬ 
trovascular system, which was in other respects of normal 
conformation, had absolutely no opening to the exterior, no 
buccal or other aperture which might establish a communica¬ 
tion between this system and the circumambient water. On 
placing the Medusa in such a position that I could examine it 
in the direction of its principal axis, it presented me with the 
appearance represented in fig. 4. The four canals were seen 
to unite in the centre without forming any enlargement or 
cavity even of the most insignificant kind. Under a high 
power the entodermic cells of the canals and their long cilia in 
