558 
PACIFIC SCIENCE, Vol. XV, October 1961 
FIG. 1. The normal tracing of the esophagus of A. calif ornica is indicated in a and the effect produced by 
0.2 mg. of atropine solution added to the 30 ml. bath is shown at the arrow. The depressing of the circular 
contractions of a ring of esophagus by 0.2 mg. atropine is shown in b. Tracings c and d show two types of 
normal tracings obtained from A. vaccaria esophagus and the effect of 0.4 mg. atropine added at arrow. 
sent when the rings of esophagus were used 
(Fig. lb), they are attributed to longitudinally 
oriented muscle in contrast to a primary circular 
muscle response. For some unknown reason the 
rapidity of contraction was increased when the 
esophagus was arranged in rings. The deep, in- 
termittent excursions are not as pronounced in 
A. vaccaria (Fig. 1 c) and may be absent (Fig. 
Id). The response of circular muscle, however, 
is consistently more rapid and more pronounced 
than is the case in A. calif ornica. 
In A. calif ornica even very small doses (0.05 
mg. in some cases) of atropine produce an im- 
mediate and unfailing but transitory contraction 
of the longitudinal muscle (Fig. la). The esoph- 
agus of Aplysia vaccaria, however, does not react 
to atropine except in comparatively large doses 
of 0.4 ml. or more (in a 30 ml. bath), in which 
case the excursions of the circular muscle are 
depressed (Fig. Id). The circular muscle of A. 
californica, as demonstrated by the muscular 
ring preparations, is noticeably depressed by at- 
ropine in even smaller doses than that required 
to depress the circular type muscle in A. vaccaria 
(Fig. lb). This depression was not noticed in 
the usual tracings of A. californica muscle since 
it was obscured by the longitudinal contractions. 
Other muscle-active drugs with specific reac- 
tions of interest in themselves (which are to 
be reported later) did not produce divergent 
results between the two species. 
In an attempt to gain an insight into possi- 
ble reasons for the divergence of reaction be- 
tween the two species, histological sections were 
made and stained with eosin and hematoxylin. 
Strongly eosinophilic bundles of coarse, cylin- 
drical muscle strands were observed in the 
esophagus of A. californica (Fig. 2a, b) . These 
strands appear coarsely striated in some prep- 
arations (Fig. 2b) and coarsely granular in 
others, the differences possibly representing 
problems in killing and fixing. The nuclei are 
larger and more sparse than those of A. vaccaria 
( Fig. 2c, d) and of the surrounding more conven- 
tional muscle of the present species. Not only 
are the nuclei three times as large but they tend 
to be arranged across the muscle strands, thus 
appearing rectangular in section. This muscle is 
