ZOOLOGY: PARKER AND TITUS 
339 
THE NEUROMUSCULAR STRUCTURE OF SEA-ANEMONES 
By G. H. Parker and E. G. Titus 
ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY 
AT HARVARD COLLEGE 
Received by the Academy, May 6, 1916 
Sea-anemones are more or less cylindrical animals that are usually 
attached to some rock or other fixed object by one end, the pedal disc, 
and carry on the opposite end or oral disc a single opening, the mouth. 
This opening, surrounded by tentacles, leads through a short oesopha- 
gus into the single internal cavity of the animal, the digestive cavity, 
and serves not only for the admission of food but also for the discharge 
of waste. The portion of the animal that connects the pedal disc with 
the oral disc is the column wall. This wall like that of the oral and of 
the pedal disc, consists of an outer layer of cells, the ectoderm, and an 
inner layer next the digestive cavity, the entoderm These two layers 
are separated by an intermediate layer of secreted material containing 
cells, the supporting lamella. The entoderm of the column wall is thrown 
into vertical folds, the mesenteries, which project from the inner face of 
this wall into the digestive cavity. In the deeper parts of both ectoderm 
and entoderm are sheets of muscle fibers by whose contraction the whole 
animal can retract greatly. This form of retraction and the reverse 
process of expansion are among the commonest activities of the sea- 
anemone. These operations involve not only the muscle layers just men- 
tioned, but also a primitive nervous mechanism associated with them. 
The muscle layers in sea-anemones are not the imdifferentiated sheets 
impKed in many of the earlier accounts of the structure of these animals, 
but fall into fairly well defined separate muscles. In the species of sea- 
anemone that we studied most fully, Metridium marginatum of the 
New England shore, there are thirteen differentiated muscles or groups 
of muscles. The longitudinal muscle of the tentacles is found on the 
ectodermic surface of these organs. The circular muscle of the ten- 
tacles covers their entodermic faces. The radial muscle of the oral 
disc spreads from the region of the mouth over the ectodermic surface 
of the disc to its outer edge. The circular muscle of the oral disc covers 
the entodermic face of this disc. The circular muscle of the oesophagus 
surrounds this organ on its entodermic side. The circular muscle of the 
pedal disc is a broad, circular sheet on the entodermic face of this part 
of the animal. The basilar muscles are radial muscles attached to the 
mesenteries where these join the pedal disc. The longitudinal muscles 
of the mesenteries extend in the mesenteries from the pedal disc to the 
oral disc. The transverse muscles of the mesenteries are at right an- 
