302 M. Krohn on the Anatomy and 
seen in one spot a spherical prominence, transparent as glass, and 
projecting beyond the pigmentary envelope; it is perhaps the 
cornea or the crystalline lens. At the circumference of the eye 
a very great number of short fibrils are perceived ; in all proba- 
bility these are fascicles of delicate nervous fibres which spring 
from the ganglion, and which seem to penetrate through the pig- 
mentary envelope in the cavity of the eye. 
Conclusions.—After having passed in review the structure of 
the Sagitta, we come at last to the question as to what place it 
should occupy in the animal series. MM. Quoy and Gaimard, 
who first noticed this animal, leave us in doubt on this point, and 
they admit that they did not sufficiently examine its structure to 
be able to pronounce an opinion. But even at present, when the 
organization of the Sagitta is better known, it 1s difficult to arrange 
it in a positive manner in any of the classes of our present 
systems. It is certain that the Sagitta is no mollusk; for al- 
though its nervous system seems organized on the general plan 
of these animals, most of the other parts of its organism and the 
habits of the animal do not seem to justify this affinity. In 
my opinion it can only be referred to the Annelides*. Here 
again great difficulties present themselves ; for, not to mention 
the absence of rings, and taking only a small number of the pe- 
culiar characters of the Sagitta, where shall we find a genus of 
Annelides provided with a hood and a similar cephalic armature, 
fins, and so remarkable a disposition of the apparatus of genera- 
tion? Nevertheless it seems evident to me that the Sagitia can- 
not enter into any other class than that of the Annelides, and 
that we must consider it as an anomalous genus, until we shall 
discover other animal forms which may connect it by gradual 
transitions of organization with some known genus of Annelides, 
or which shall completely separate it from this class of animals. 
EXPLANATION OF PLATE IV. B. 
In order not to encumber the figures with letters, we shall only indicate 
a single organ or a single half of an organ, when there is a pair of them. 
Figs. 3, 4,5 and 6 represent the head magnified from ten to twelve times 
* Having had occasion to observe the Sagitta bipunctata during my last 
voyage to Messina, I think I may say that I do not in any way share the 
opinion of M. Krohn on the natural affinities ofthat animal. I find nothing 
in its organization which can Jead me to consider it as an Annelide, and I do 
not doubt that it is a mollusk, having in certain respects a great analogy to 
he Firole. It seems to me that the part designated by the author under 
the name of head is formed principally by the fleshy bulb of the mouth car- 
rying the dental armature, and that it is the fold cailed hood in the prece- 
ding memoir which represents the head. ‘The curious arrangement of the 
organs of generation noticed by M. Krohn constitutes the chief anomaly in 
the structure of this animal.—Mitne Epwarps. 
