Differences in Sea Hares — Winkler and Tilton 
559 
contrasted with the less eosinophilic, more un- 
dulatory muscle of the circular (Fig. 2a) and 
A. vaccaria type muscle (Fig. 2c, d) , which is 
very heavily nucleated. While strands of a type 
of muscle which seems morphologically to be 
somewhat similar to the former type of muscle 
appear sparsely in the crop, and to even a lesser 
extent in the area between the gizzard and 
"stomach” of the digestive tract in A. calif ornica, 
none of the eosinophilic muscles observed in 
other parts of the digestive tract of A. vaccaria 
possessed the distinctive tubular shape with the 
vacuolation, striation or granulation, and lack 
of undulatory characteristics. 
DISCUSSION AND CONCLUSIONS 
While it might be tempting to assume that 
the histological differences represent the imme- 
diate cause of the divergent pharmacological 
reactions observed, they are better interpreted as 
visible, easily demonstrable, morphological dif- 
ferences which parallel and are closely associated 
with neurohumoral and even biochemical dif- 
ferences which are themselves the underlying 
mechanistic causes. This is especially true since 
the effect of atropine on conventional tissue sys- 
tems is thought to be on the neuromuscular re- 
ceptors. The contractatory response observed in 
A. calif ornica appears to be the transitory result 
of stimulation, since the mechanical stimulation 
of washing will produce similar contractions. 
However, the sensitivity to this chemical stimu- 
lation is very great, being as low as 0.05 mg. 
atropine placed in the 30 ml. bath — a concen- 
tration of 1:6x10 s . Such a sensitivity represents 
a very delicately balanced chemical system. 
FIG. 2. A. calif ornica: a, cross section; b, longitudinal section. A. vaccaria: c, longitudinal section; d, cross 
section. The midsection of the esophagi were used for cross sections. 
