i8 3 
examining of the mesenteries I made horizontal sections by preference (across the actinopharynx), 
while, according to Brook, the mesenteries could be best studied in these sections. -— When the 
material was abundant, I also made vertical cross-sections (at right angles with the transversal 
axis of the polyps), while in rare cases also vertical longitudinal sections could be made (at 
right angles with the sagittal axis of the polyps); however in the latter case the axis itself, 
which was cut over its full length, gave very great difficulties. — Before describing the sections, 
I have to make a few remarks about the direction in which the polyps are attained, because 
of the peculiar position of the polyps on the axis. Rarely the oral cone is at right angles with 
the axis with an actinopharynx, which descends as a straight tube; in this case only the mesen¬ 
teries could be studied best in horizontal sections. But usually the polyp is situated as is figured 
in fig. 254 (vertical longitudinal section, schematized). The oral cone'is curved distally so that 
the mouth is not horizontal; the lateral tentacles are 
curved around the mouth and the distal pair is smaller 
than the proximal pair. The actinopharynx is in its 
upper part curved distally, but in its lower part this 
curve is directed proximally. In fig. 254 the primary 
transversal mesenteries (blackened) are attained over 
their full length. It will be clear that in this case, in 
horizontal sections, the upper part of the mesenteries 
is cut obliquely instead of across, and so is less efficient 
for the study of the direction of the musclefibres. 
This part of the mesenteries will be attained in a 
vertical cross-section of the polyps in a manner far 
more efficient to show the longitudinal musclefibres. 
The same longitudinal fibres in the lower part of the 
mesenteries, will be especially visible in horizontal 
sections and not in vertical cross-sections. As the 
mouth is usually neither horizontal, nor vertical (as is 
figured in fig. 254) it is easy to see why the muscle system on the mesenteries, found by me, 
was not at all or not clearly observed by other authors, or that they were not able to observe 
a special direction of the musclefibres. In the horizontal sections though, made by Brook for 
preference, he cut the mesenteries always obliquely in their upper part, where the musclefibres 
are principally developed. — It is also possible, through the peculiar curved shape of the 
actinopharynx, that in part of the series of sections the longitudinal musclefibres are attained 
in a manner which makes them clearly visible, while in an other part of the same series the 
transversal musclefibres are more conspicuous, and so, if one makes no allowance for the curve 
of the actinopharynx, they give the impression of being also longitudinal musclefibres, while 
apparently the direction of the sections is not changed with regard to the axis of the 
actinopharynx. It is also possible that for the same reason I some time wrongly supposed that 
the longitudinal musclefibres on both sides of the actinopharynx were not applied to the same 
side of the mesenteries of one and the same pair. 
Fig. 254. Schematical vertical longitudinal 
section through a polyp. 
The oral cone bends distally (to the left). The 
primary transversal mesenteries are black. 
The free border of the actinopharynx is dotted. 
The lateral tentacles which are lying before the 
plane of the figure, are indicated by a line of dots 
and crosses; the distal lateral tentacle ( dist.l .) is smaller 
than the proximal one ( prox. /.); m. f. mesenterial 
filaments; act. actinopharynx; g. gastral cavity. 
