M. C. Mereschkowsky on the Hydrotda. 255 
once I observed in a perfectly round nucleolus more than one 
nucleolulus, or rather a single nucleolulus in the centre sur- 
rounded by five or six’ very small granules forming an aureole 
round the centre. 
As I observed all these stages of development in ova which 
had not issued from the sporosac, and, moreover, there was 
not a male individual in the neighbourhood, all the processes 
described took place in ova not yet fecundated. It would be 
interesting to know why there is all this enormous complica- 
tion. But as yet the facts are too few to permit us even to 
think of an explanation. 
Lastly, this hydroid has offered me another interesting fact 
which [ will mention. For the purpose of observing the 
development of the Meduse I placed a branch of Obelia 
flabellata upon a slide, and laid over it a covering-glass ; the 
sea water by evaporating became salter and salter, which 
(and perhaps also the want of oxygen) appeared to affect the 
organism in a singular manner. In a short time I remarked 
that the coenosare of the stem detached itself in fragments of 
different sizes, especially near the end. First of all there 
appeared a constriction in a particular spot; this constriction 
became deeper and deeper ; and finally the two parts separated 
entirely, so that the end of the stem formed a fragment quite 
independent of the colony. ‘The two parts contracted, moved 
away from each other, and became rounded at their ends, so 
as to leave no trace of their lesion (Pl. XIII. fig. 16); the 
ectoderm and the endoderm recurved at the newly formed end 
just in the same way as in the end of the stem: the cavity 
was very distinct ; and I could even observe the movement of 
nutritive granules, which I also saw in perfectly fresh 
specimens. Except wanting the mouth and cilia, this little 
cylinder much resembled a planula. In fig. 17 is repre- 
sented a hydrotheca not yet completely developed, closed at 
its future aperture, in which the ccenosare is contracted, not 
into a cylinder, but into a perfectly regular globular form, 
with a cavity, and surrounded by two layers. At one spot a 
very fine and colourless membrane, evidently produced by the 
ball, is seen to detach itself; this, no doubt, is a new layer of 
perisare formed by the ectoderm ; and I believe that in the 
other cases the perisare is also present, but that in them it 
adheres very closely, for which reason it cannot be perceived. 
What is the signification of these structures? For what 
purpose are they formed? Is it not a sort of encysting, 
analogous to the process so often met with among the Infu- 
soria? Are not these fragments of the Hydroid the result of 
its dismemberment, caused by the evaporation of the water ? 
