20 Comparative Neurology. [ January, 
As illustrative of undifferentiated faculties it may be mentioned 
that by the Gregarine food is taken in by endosmotic processes 
at the surface. Any place in the protoplasm can act as a digestive 
cavity by enveloping and absorbing nutritive matter. 3 
It is the simpler view, entertained by some (in opposition to. 
the delamination precedence theory), that the form which preceded _ 
the gastrula was a one-layered vesicle which, by invagination, — 
produced the endoderm from the ectoderm. While the ectoderm 
was undifferentiated, all parts of the cell were assimilative. In_ 
the gastrula stage the endoderm acquired specific ingestive facul-— 
ties. Differentiation of the purely ingestive proceeds thus from — 
the intestine, while the ectoderm remained in contact with the 
more variable conditions of the environment, and developed the 
greatest qualitative sensory and motor organs. The entire ner-_ 
vous organization, in its earliest condition, answers to that por- 
tion which, in Vertebrata, presides over the vermicular motions 
of the intestines, and the correlated respiratory and circulatory 
structures—the sympathetic nervous system. This, therefore, we 
may entitle the First System. As soon as the enteron is created, 
by folding in of the ectoderm, qualitative development of this 
First System is restricted to such functions as are more clearly 
nutritive, as, when the blood vascular system is differentiated from 
the mesoderm, the vaso-motor nerves are derived from or added 
to the sympathetic, and exactly in the ratio of development of th 
viscera so does the First System differentiation proceed. 
Pe GT ie ee ae ee RT a aS age ae ag ee 
In high forms of Invertebrata, but more pronounced in Verte 
brata, the viscera, and consequently the First System of nerv 
occupy an inferior position, properly termed ventral, while as 
broad rule the upper surface of the animal comes most in conta¢ 
with varying molecular motions of the outer world. Hence, W 
may say that it comes to be a law, that from the dorsal to tt 
ventral parts of the animal, ingoing impressions proceed, and, ‘ 
necessity, progressive development must occur, by superimpt 
tion upon the ventral system. 
_ The first appearance of a Second System, equivalent to th 
spinal cord (segments coalesced) of Vertebrata, is indicated 1 
ganglionic enlargements upon the afferent nerves of the Firs 
System. | 
This is apparent in the oyster, whose anterior ganglia (A) ar 
placed upon the fibers leading to the principal ganglion of t 
