1881. ] Comparative Neurology. 21 
body. (Ina typical embryonic, not phylogenetic sense, for the 
oyster is a degraded Lamellibranch.) 
This appears to be a specialization of the tactile sense, with 
reference to its uses anteriorly in food discrimination and inges- 
tion, involving ciliary prehension and control of the valves. In 
Pecten further quantitative development of a Second System pro- 
duces the pedal ganglion (C), also related to the touch sense. 
The cilia of Protozoa subserve ingeStive as well as locomotor 
purposes, and show the relationship of ingestive and general mo- 
tions, and that the locomotor ability is often derived from the 
prehensile ingestive. In the free Rotifer this is quite apparent. 
As the segments increase the sub-cesophageal ganglia multi- 
ply ; the first set of ganglia become relatively ventral and preside 
over nutrition, while the second set, relatively dorsal, indicate 
progressive differentiation, as control of a pedal extremity or some 
special organ related externally. At the same time this dorsal 
ganglion is connected always with the ventral system. Fusion of 
these segmental ganglia with each other, or with ganglia of other 
systems, produce confusing appearances. This fusion of systems 
is most clearly seen in Vertebrata. 
The vibrating molecules which produce the undifferentiated 
impressions upon lower Protozoa may be considered as causing 
purely tactile excitation. Just as the waves that dash the primi- 
tive animal about differ from the ripples that bring it food, only 
in degree, so the differences between impressions must be 
regarded, All sensation being related to molecular motions, and 
all special sense organs being derived from indifferent primaries. _ 
Otocysts in their simplest form are connected directly with oe 
nerves, as are the pigment granules which eventually develop into 
eyes. Prof. Alf. M. Mayer shows that the fibers of the antenna 
of the male mosquito vibrate sympathetically to the notes of the — 
female mosquito, and that the vibrations of the insect’s antenne 
may teach it the direction of sounds (thus allying this sense to — 
