122 
Fig. 1. Ritteriella picteti, aggregate form. AO, atrial 
opening; CF, dorsal tubercle; END, endostyle; G, gill; 
GG, ganglion; FIM, dorsal horizontal muscle; M, 
mouth; I-VI, body muscles. 
Muscles: The body muscles (Figs. 1, 2) 
may be asymetrically arranged. There are 
usually six body muscles on each side of the 
animal although specimens have been found 
with seven on one side (Fig. 2). Body muscles 
I and II are joined over the dorsal half of their 
course, separating laterally, whereas III and 
IV are joined dorsally over a short portion of 
their course and contact the bundle formed 
by muscles I and II in the same general area. 
Muscles V and VI are also in contact over the 
dorsal portion of their course. Laterally, mus- 
cles IV and V may approach closely. Muscle 
VI has an anterior branch in front of the gut 
and a posterior branch which joins its mate 
from the opposite side over the gut nucleus. 
There is a broad, independent muscle running 
along the base of the posterior process. The 
atrial muscles resemble those of K. amboinensis. 
PACIFIC SCIENCE, Vol. VIII, April, 1954 
There are four delicate sphincters attached t 
laterally to a delicate retractor muscle. This ' : 
muscle then attaches to a heavier retractor I 
which receives the attachment of the heavy j 
basal sphincter. The retractor finally attaches 
to muscle VI just before the sixth muscle ' 
divides. The oral musculature (Fig. 3) in- 
cludes a single oral retractor laterally on each 
side and three sphincters on both the upper | 
and lower lips. The sphincters of the upper |l 
lip include a wide muscle which is discon- |' 
tinuous medially, Ui, a narrow muscle, U 2 , i 
and a wide muscle, U3. The sphincters of the | 
Fig. 2. Diagrammatic representation of some varia- 
tions found in the arrangement of body muscles of 
Ritteriella picteti, aggregate form: I-VI, body muscles. 
