300 M. Krohn on the Anatomy and 
all im their state of maturity. According to this, it is scarcely 
doubtful that the seminal fluid introduced into the ovarian cavi- 
ties belongs to them, and that, consequently, the Sagztta fecun- 
dates itself. But by what means is the seminal fluid transferred 
from the male into the female apertures, and how does it pass 
over so great a space? It is difficult to say; I can only offer 
presumptions on this point. If we suppose that the water serves 
as the vehicle, we are scarcely more advanced, as it is necessary 
to explain how the seminal fluid is condueted into the ovary. 
Shall we admit that it is propelled by currents produced by the 
movements of the vibratory cilia, existing either toward the en- 
trance into the ovaries or at the mouth of their excretory ducts ? 
But I have never been able to perceive, in any part, these vibratory 
cilia in the female genital apparatus. It is therefore probable 
that the transference of the seminal fluid is effected by the alter- 
nate approach of the male and female apertures; and this may 
take place by means of the tail being curved under the body. 
Nervous system :—Cephalic ganglion.—The principal ganglion 
of the head, or the cephalic ganglion properly so called, is si- 
tuated in the middle of the upper surface of the head and at a short 
distance from its anterior margin, immediately beneath the skin 
and above the pharynx. It is flattened, nearly hexagonal, and, 
in adult individuals, it is about a quarter of a millimetre in ex- 
tent. It sends out two pairs of nerves, one anterior, one poste- 
rior, and communicates with the trunk or ventral ganglion by 
two strong and elongated cesophagian commissures. 
Each of the anterior cephalic nerves is detached from the an- 
terior margin of the ganglion, remains at first almost parallel to 
its congener, is then directed toward the prominence furnished 
with bristles already mentioned, penetrates into the fascicles of 
some muscles, and finally loses itself in the muscle of the hooks 
of the corresponding side, after having become swelled into a 
kind of ganglion, in the vicinity of this muscle. From this 
swelling several filaments radiate, which divide themselves in the 
muscle. 
The two posterior cephalic nerves, which spring from the pos- 
terior margin of the ganglion, exhibit remarkable peculiarities. 
They are larger and more elongated than the anterior ones, re- 
main, throughout their course, just beneath the skin of the upper 
surface of the head, and extend to the limits of the trunk. They 
diverge considerably from thew very commencement, and curve 
finally into a circle toward the median line of the head, where 
they anastomose, forming a kind of nervous arcade. At a little 
distance from their or igin, each of these small trunks furnishes an 
optic nerve, which will be considered hereafter. 
Ventral ganglion. —This ganglion is situated in the middle of 
