198 ON THE NERVOUS SYSTEM OF THE NEMATODA. 
met with to a mode of dissection peculiar to himself, and the 
want of which (though extremely simple) has hitherto pre- 
vented the successful prosecution of the research. The central 
nervous system constitutes a ring closely surrounding the 
cesophagus, but not attached to it. On the other hand, it is 
firmly connected by various processes with the walls of the 
body. This arrangement suggested the mode of dissection 
to be followed for its due display, and which is thus de- 
scribed :—Cut off a portion of the anterior end of an Ascaris 
megalocephala, for example, about half an inch long; then, 
with a fine and sharp pair of scissors, slit up the walls of the 
body together with the cesophagus; then cut off the lips and 
remove the cesophagus, and spread out the walls of the body, 
and the central nervous system will be seen lying uninjured 
on their inner surface. The essential part of the proceeding 
is the slitting up of the cesophagus as well as the walls of the 
body. The preparation is much improved by the boiling of 
it for a short time in dilute acetic acid, after which the cuticle 
can be readily removed and the specimen rendered transparent 
by glycerine. Specimens of A. megalocephala not fully grown 
are better fitted for examination than older ones, owing to 
their greater transparency. This dissection affords the 
readiest and easiest view of the entire nervous system, but in 
order to learn its minute structure numerous transverse 
sections are requisite. These sections must be very carefully 
made with the sharpest possible knife. To allow of their 
being properly made, the worm must be hardened, first in 
spirit, and afterwards in chromic acid. 
Dr. Schneider’s researches have been carried on chiefly in 
Ascaris megalocephala and Oxyuris curvula, In A. megalo- 
cephala the nerve-ring is placed about 2 mm. behind the oral 
orifice. From it six cords are given off in front; four of 
these (nervi submediani) arise nearly in the middle, between 
the border of one of the lateral intermuscular spaces and the 
middle line, though rather nearer the lateral space. The roots 
commence with a broad base, which gradually narrows into 
the slender cord. Two other nerves (a. daterales) lie in the 
middle of the lateral intermuscular spaces. These nerves are 
completely imbedded in the substance of the lateral space, 
and they may, with some pains and trouble, be at once dis- 
sected out, or may be seen more readily, but still distinctly, 
in simple transverse sections. Two strong nervous cords 
pass backwards; they arise on the ventral side of the ring, 
one on either side of the ventral line, towards which they 
tend in a sort of arch and are continued a short distance, but 
they cannot be traced beyond the arched anastomosis of 
