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“lash” of the Noctiluce. In the second place, a peculiar 
mode of movement is observed, which has probably, as end 
and result, the progressive elongation of the arm. The ex- 
tremity of the prolongation is spontaneously reflected, and 
then one observes the reflected part gradually elongating ; 
whilst at the same time the point of flexion gradually ap- 
proaches the body of the cytod (fig. 6’, 6”). The straight 
part of the arm appears to contract at the same time, and a 
very slight transverse striation is seen to appear in this part 
of the prolongation (6” and 6”). Then suddenly and briskly 
the entire arm recovers its position, as though it were made 
of some eminently elastic substance; and at the same time 
the granular and fluid protoplasm of the centre of the cytod 
rush, forming a sort of current, into the interior of the arm. 
It is clear that these movements, which succeed at short 
intervals, ought to result in the progressive elongation of this 
arm. I have been able to establish the fact of this gradual 
elongation by observing the same cytod during several hours. 
The only other modifications which appear in the character 
of the prolongation are the pinching in of its basilar portion, 
and the accumulation of nutritive granules in its terminal 
portion, which I shall designate “ cephalic.” 
When the mobile arm has attained a certain length, it de- 
taches itself from the body of the cytod, and, becoming free, 
executes undulatory movements in the manner of a Nematoid 
worm. I have not seen this arm actually detach itself from 
the cytod, but quantities of these filaments are found moving 
freely in the intestine by the side of the cytods, on to which 
they are also found fixed by one of their extremities. 
To elucidate completely this part of the evolution of the 
Gregarine, we ought yet to inquire whether all the body of 
the cytod is not employed in the elaboration of one of the 
free mobile filaments. 
It follows from the facts which I am about to enumerate 
that one and the same cytod gives rise to two filaments, 
destined each to become a Gregarine, that is to say, that two 
Gregarine always are produced from a single cytod, which, 
on this account, I have called the “‘ generating cytod.” The 
first to attain maturity is the mobile arm, it detaches itself 
from the cytod before the second—the right arm—attains the 
phase of mobility. On the other hand, all that remains of 
the body of the cytod is employed in the maturation of this 
second arm. 
Among the cytods with two arms, one inert, and the other 
extremely mobile, some cytods are found which have only a 
single prolongation. Of these, some possess an inert arm, 
