560 
Moreover, the mechanism is of special interest 
since it is unique among known muscle prep- 
arations in that it is stimulated rather than de- 
pressed by atropine. 
The drug reaction and histological difference 
accentuates the divergence present within the 
genus. A. vaccaria belongs to a large and wide- 
spread subgenus ( Aplysia ), while A. calif ornica 
(subgenus Neaplysia ) is unique to the Calif or- 
nias. When it becomes possible to study com- 
paratively the members of the two other sub- 
genera 2 ( Varria and Pruvataplysia ), a taxonomic 
generalization may be possible. However, Bot- 
tazzi ( 1898) in his physiological study of the 
esophagus indicated that A. limacina (almost 
certainly A. fasciata of subgenus Varria ) was 
much more atonic than the close relative of A. 
vaccaria ( subgenus Aplysia ) with which he also 
worked. Since it is thought that A. calif ornica 
is an offshoot of this subgenus Varria , and since 
its esophagus is far from atonic by any inter- 
pretation, it may be that the musculature of the 
former has diverged considerably from its fore- 
runners. 
It would also seem quite probable that more 
comparative studies of the tissues of the species 
contained in other genera of animals would re- 
veal occasional divergences of at least equal 
magnitude. Such a possibility cannot safely be 
overlooked in experimental biology in any of 
its phases, and accentuates the need for accurate 
taxonomy before proceeding with studies which 
may be of a nontaxonomic nature. 
2 Specimens of esophagus tissue from these subgen- 
era were kindly supplied from existing museum mate- 
rial on hand by Dr. N. B. Hales but, unfortunately, 
the conventional preservation method employed by the 
collectors was not adequate for any type of conclu- 
sions. 
PACIFIC SCIENCE, Vol. XV, October 1961 
SUMMARY 
1. The normal pattern of esophageal contrac- 
tions in Aplysia calif ornica consists of short 
rapid contractions attributed to circular muscle, 
interspersed at intervals by deep excursions at- 
tributed to the longitudinal musculature. These 
secondary contractions are less pronounced and 
less regular in A . vaccaria. 
2. Atropine causes marked contraction of the 
esophagus in A. calif ornica, even in low con- 
centration, but in A. vaccaria it depresses circu- 
lar activity in higher concentrations. 
3. The esophagus of A. calif ornica has longi- 
tudinal bundles of cylindrical muscle appearing 
coarsely striated or granular. These have not 
been found in A. vaccaria , and are suggested as 
being associated with the mechanistic cause for 
the differences in reaction noted. 
REFERENCES 
Bottazzi, Phillip. 1898. Contributions to the 
physiology of unstriated muscular tissue, Part 
IV. The action of electrical stimuli upon the 
oesophagus of Aplysia depilans and Aplysia 
limacina . Jour. Physiol. 22: 481-506. 
Cooper, j G. 1863. On new and rare mollusca 
inhabiting the coast of California. Proc. Calif. 
Acad. Sci. 3: 57. 
Hogben, Lancelot T. 1924. Studies on inter- 
nal secretion, III. The action of pituitary ex- 
tract and adrenaline on contractile tissues of 
certain invertebrata. J. Exp. Biol. 1 : 487-500. 
Straub, Walther. 1907. Zur chemischen 
Kinetic der Muscarinwirkung. Pfluger § Ar- 
chiv. 119. 
VON Brucke, E. Th. 1905. Zur Physiologic der 
Kropfmuskulatur von Aplysia. Pfliiger’s Ar 
chiv. 108. 
