Perhaps it is not too much to say that the eidoscopic
eye first awakened the slumbering animal mind, for its reflex effect
upon the supra-oesophageal ganglion cannot be over-estimated. The
animal will very soon begin to think.
Between the turbellarian and the annelid many aberrant lines
diverged. Some of these attained a comparatively high level and then
seemed to meet insuperable obstacles, while others came to an end or
turned downward very early. Three of these demanded attention, those
leading to mollusks, insects, and vertebrates. And it is interesting
to notice that the fundamental difference between these three lines
was the skeleton, or perhaps we ought to say it was the habit of
life which led to the development of such a skeleton.
The mollusk took to a sluggish, creeping mode of life, under an
external purely protective skeleton; the insect to a creeping mode
of life, with an external but almost purely locomotive skeleton; the
vertebrate kept on swimming and developed an internal locomotive
skeleton. And it must already have become clear to you that the
destiny of these different lines was fixed not so much directly by
the skeleton itself as by its reflex effect in moulding the
muscular, and ultimately the nervous, system.
The insects formed their skeleton by thickening the horny cuticle of
the annelid.
Pages:
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149