16 Desor on the Development of Polynée. 
erto, independent motion has generally been considered as 
the strongest criterion of animal life, and in order to sustain 
this view, naturalists have attempted to establish various arbi- 
trary distinctions between animal motion and that of certain 
seeds, especially the sporules of Conferve. Now we have 
here vitelline spheres that move in a manner of their own, 
different from that of the animal within, and, as it seems, 
under the influence of a power quite independent of the con- 
trol of the animal, though the means by which this motion is 
performed are similar, that is to say, by ciliz, like those of 
the animal itself. We may, therefore, conclude that this is a 
motion, which, though dependent upon life, does not belong 
essentially to the individual. 
. The foregoing investigations were made in East Boston | 
during the months of February and March, 1848, with a mi- ` 
croscope belonging to Professor Agassiz, with whom I had 
the pleasure of discussing several of the results obtained. An 
abstract was communicated to the Boston Society of Natural 
History at the session of the 5th of July, 1848. To my 
friends, Dr. S. Cabot and Elliot Cabot, Esq., I am highly in- 
debted for many valuable suggestions, and also for having had 
the kindness to revise the proof of this paper. 
EXPLANATION OF THE PLATES. 
(The magnifying power is 50 diameters when there is no higher power indicated.) 
Puare I. Fic. 1. Nemertes obscura. Desor. Nat. size. 
Fic. 2. String of eggs of Nemertes obscura. Nat. size 
Fic. 2. a. The same 10 times magnified, to show the disposition of the 
flasks. 
Fic. 3. A single flask, with four yolks. 50 diam. 
Fic. 4 and 5. Single yol compressed, showing the oily liquid in form 
of a hernia, a, on the margin 
Fic. 6 and 7. The same yolks more compressed, so as to divide the 
hernie into several small drops (6). 
Fic. 8. Portion of a flask 400 times magnified, showing the: cellular 
