NOTES AND MEMORANDA. 
333 
blunt extremity (which is still adherent to the point of gemmation), 
than to the other end. This extremity is always foremost when the 
freed gemma swims upon its plane surface propelled by the undula- 
tions of the flagellum which trails behind it. One or two pulsatile 
vacuoles or vesicles of *004 mm. diameter are seen in the cellular 
body of each gemma between the plane surface and the nucleus. This 
vesicle is absent in the adult. 
No observer has been able up to the present to follow the evolu- 
tions of Noctilucie from the gemma state up to that of the adult indi- 
vidual. It is not yet known whether the flagellum of the gemma from 
• 10 mm. to • 12 mm. in length remains like the flagellum of the adult, 
which is only *06 mm. to *07 mm. long. The smallest Noctilucas 
which I have seen were of • 15 mm. diameter, spherical, without mouth 
or infundibular depression, and with neither flagellum nor tentacle. 
I have followed the formation of the mouth at the level of the 
nucleated cellular body adherent to the internal face of their wall. 
It begins by a linear wrinkle of the latter, which is thickened a little 
on each side of this fold by the production of two or three mammil- 
lated projections. This thickening becomes gradually yellowish, and 
takes the form of the lij)s of the buccal slit in the adult. These phe- 
nomena last about three-quarters of an hour, after which the lips open 
a little from time to time. Then begins the formation of the infundi- 
bular depression and of the rectilinear dorsal fold, as well as that of 
the tentacle. That of the flagellum only takes place after the comj)lete 
development of this latter organ. 
Let us note that some Noctilucfe are found scarcely larger than the 
greater number of the others which are anatomically double, that is to 
say, provided with two cellular bodies, with two alternate buccal slits, 
each accompanied with corresponding tentacle and flagellum. It is 
probable that they proceed from some gemma in which the fission 
raising their number from 128 to 256, or from 256 to 512, has failed, 
whilst it took place in the others ; a gemma which nevertheless has 
continued to develop like the others. 
The fission of the Noctilucm has been pointed out by M. de 
Quatrefiiges (1850), and by Krohn (1852), who has seen that it begins 
by the fission of the nucleus, since better studied by Brightwell. 
The fission of the nucleus presents the same phases as at the time of 
its first division in the cases of gemmiparity. The total division of 
the Noctiluca takes place in such a manner that, once comj)lete, each 
of the two new individuals has a buccal slit, in which one of the lips 
has grown from one of those of the buccal slit of its generator. A 
tentacle is developed on the side of the mouth of each new Noctiluca 
from the end of the total fission, or immediately after the sej^aration 
of the two new individuals. It is about an hour before the freed 
organ begins its movements. 
In all cases, the production of the tentacle begins by the formation 
of a short prolongation of the yellowish substance of the cellular body 
which raises the tegument near one of the lips of the buccal slit, 
showing itself a little. Below tliis prolongation and in continuity 
with it, a second is raised, conoidal at first, and gradually taking the 
