154 
time it will be admitted that, at least in this instance, we 
have some very definite data to argue from. 
In the tissue I have figured there are no capillary vessels ; 
only one kind of nerve-fibres ; only one nerve-centre ; con- 
nective tissue between the muscular fibres, in which very fine 
nerve-fibres can be followed ; no sarcolemma to confuse us ; 
very fine muscular fibres, some less than the xoVo^ 1 °f an 
inch in diameter, over and under which the nerves can be 
seen to pass ; and lastly, masses of germinal matter belonging 
to (a) the muscular tissue, (b) the nerves, and ( c ) the connective 
tissue. Moreover, these tissues form together a very thin ex- 
pansion, one surface of which, during life, is in contact with 
the blood, while the other is free within the pericardial cavity. 
The facts ascertained by a careful examination of the speci- 
mens almost compel us to infer that the fibres leaving each 
nerve-cell are afferent and efferent. And it is really not 
venturing far beyond the conclusion to which direct observa- 
tion leads us if we conclude that a nerve-fibre leaves a nerve- 
cell, and, after ramifying amongst muscular fibres, passes 
near to the inner surface of the auricle, and then returns to 
the same cell. An impression made upon the last part of the 
fibre, as from the mere stretching to which it would be sub- 
jected by the dilatation of the auricle with blood, or by the 
blood itself affecting the current traversing it, would cause 
• momentary change in the cell, and an augmentation of the 
intensity of the current sufficient to cause sudden contraction 
of the muscular fibres. The changes' which caused the con- 
traction ceasing, the muscular fibres would again be relaxed - , 
after which more blood would be poured into the cavity, and 
the distension of its walls would bring about a repetition of 
the same phenomena as before, which would be immediately 
followed by contraction, and so on. 
The spherical and oval gangli on-cells , as distinguished 
from the angular and caudate nerve-cells, are sufficient for 
the production of reflex action. This class of cells is the 
only one that exists in the invertebrata where reflex actions 
are remarkable. These cells are highly developed in the lower 
vertebrata, and are well formed and active in mammalia and 
man at a period of development when the angular and 
caudate cells are still in an embryonic and incomplete state, 
and, as yet, incapable of performing any office or work. 
