EN Desor on the Development of Polynoe. 
spontaneous, nevertheless it seemed to me different from the 
motion of any embryo with which I was acquainted. Their 
manner of moving was abrupt and jerking, somewhat unlike 
voluntary motion, but which reminded me strongly of the 
motion of the sporules of Confervee, which I had formerly 
observed at Neuchatel, and described in the Proceedings of 
the Helvetian Society.’ 
The motion of the embryos seems to be incessant, as long 
as they have plenty of water to swim in, but the rapidity is 
variable. On placing them on the glass so as to leave them 
nearly dry, | succeeded in stopping them for a moment. 
What was my astonishment when I saw that the two red 
spots, which are visible very early, (fig. 36), were not situated 
on the surface, but belonged to an embryo that was lodged 
inside of this moving sphere, (fig. 38), and had an independ- 
ent motion. With the help of the two red spots I could 
easily ascertain the real position of the embryo. "The next 
day the embryo was more defined, (fig. 40), and 1 could dis- 
tinctly see it contracting itself inside of the sphere,’ like the 
embryo of the Nemertes in its envelop. 
The embryos remained in that state for several days, when 
I saw that their motions were more sluggish; some of them 
remained even motionless at the bottom of the vase. On ex- 
amining them in that state, I found that the envelop was torn, 
the threads were hanging down, and there was a swelling like 
a large hernia projecting, (fig. 41.) I soon perceived that 
it was the embryo about to escape. This operation is not per- 
formed without some difficulty, if we may judge by the 
amount of time that is necessary for the embryo to disengage 
itself, (sometimes 5 and even 10 minutes.) It is worth notic- 
