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of an insignificant deviation in distance on both sides, not even 10/^, I suppose. The
exact proportion can not easily be given in fixed numbers, the torsion of the tail pre-
venting its being placed in one plane.
The two spicules are exceedingly different in shape and size, one being only
93 fi in length, whereas the other measures 528 //, or nearly 6 times the length of
the first one. The shorter spicule is sword-shaped with rounded point. In the
proximal end it reaches its maximal width, the diameter being about 9/^; af ter
which it is tapering evenly towards the tip, being at the same time sHghtly curved.
It seems to be hollow throughout the length, presenting along each edge a double
contour with distinct transverse striæ. Thus, in optical section it has the aspect of
two converging rods, meeting in the end and transversally striated (P. IV fig. 31).
The above description applies to the spicula when seen in profile. In a preparation
dorso-ventrally compressed, it is squeezed together and presents quite another appear-
ance. It then apparently will have its maximal width at the middle, showing a
longitudinal thickening which in faet will be nothing but a fold due to the pres-
sure (PI. IV fig. 24). The ring-shaped profile of the proximal end of the spicule as
seen on the fig. distinctly shows the interior cavity, mentioned above. The longer spi-
cule nearly has a uniform width throughout its length, but for a small dilatation in
its proximal end. It contains a cavity similar to that of the thicker spicula. In op-
tical sections, however, the slender spicula appears as two parallel lines, turning
off each other at some distance before the tip and meeting together in the very
end of the spicula, — whereas the thicker spicula were seen as two converging
rods meeting in the distal end. In other words: The point of the longer spicule
most of all resembles a strongly twisted piece of wire (PI. IV fig. 30). When
seen under high magnifying power the point of the long spicule looks as if surrounded
by a fine membrane, in optical sections resembling a ferrule of a sword (PI. IV fig. 30),
or it might be considered somewhat similar to the so-called "cutter" in certain Poly-
chæte setæ. When the spicules are at rest and in their natural position in the worm,
the tips are almost converging or at any rate placed quite near to one another,
whereas for the rest the spicules are diverging and form a distinct angle. In the
fig. 24 the shorter spicule is retracted unnaturally far. Most frequently the longer
spicule will be seen protruded, stretching out of the anogenital duet with almost half
its length. It will then be strongly bent, the protruded distal part at a right
angle to the proximal part. The curving takes place somewhat within the anus. The
shorter spicule was never found protruded in any case.
Under high magnifying power both spicules appear to be surrounded by a most
pecuhar apparatus which shall now be explained, without laying claim to any com-
plete correctness. Especially it is possible that the thing found extends further back or
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