ZOOLOGY: PARKER AND TITUS 
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the tentacles of Metridium. Here ectodermic sense cells connect di- 
rectly with the underlying longitudinal muscle fibers and thus these 
fibers are brought into action without the intervention of so extensive a 
network as in the former instance. 
What seems to be a third type of neuromuscular mechanism is seen 
in the circular muscle of the column of Metridium. If the exterior of 
the column of this animal is stimulated mechanically, retraction gener- 
ally follows. If the spot stimulated is anesthetized by allowing a few 
crystals of magnesium sulphate to dissolve on it and it is then stimu- 
lated, general retraction does not result but in the course of a minute 
or so a band formed by a local contraction in the circular muscle of the 
column appears and gradually spreads around the column. This band 
of contraction then slowly disappears. The reaction is apparently 
due to the direct stimulation of the circular muscle of the column, a 
muscle which from other grounds is known to be open to indirect stim- 
ulation probably through the nervous network. 
A fourth type of muscular activity is seen in the longitudinal muscles 
of the acontia. If these filamentous organs are detached from a Merti- 
dium, they will five hours in ordinary sea-water moving about in tortu- 
ous lines by means of their cilia. If such free acontia are stimulated 
mechanically, they slowly tangle themselves up and afterwards slowly 
untangle. If now they are subjected to what would be thorough anes- 
thetization with chloretone and are again mechanically stimulated, 
they tangle themselves up as before. Apparently their muscle is en- 
tirely independent of nerves and under ordinary conditions is brought 
into action by direct stimulation. 
These four types of muscle action are of phylogenetic significance. 
The last mentioned, that of the longitudinal muscle of the acontium, is 
the most primitive and resembles the type found in sponges in that it 
is slow in action and not under nervous control. The next in advanc- 
ing complexity is the circular muscle of the column partly independent 
and partly under nervous influence. The third, the longitudinal sys- 
tem of the tentacle, is a well defined union of sense cells and muscle 
fibers and is relatively quick in action. Finally the most complex type 
is the sense cell, complex nervous network, and muscle fiber as first 
described, a quickly responding, most highly differentiated example. 
These four types show that the neuromuscular mechanism of sea anemones 
is by no means so simple and uniform as was originally supposed but em- 
braces a variety of structural conditions which serve different purposes 
and probably represent evolutionary steps. 
The full paper will be published in the Journal of Expemnental 
Zoology. 
