form-perceiving, eidoscopic
organ. The eye was short of range and its images were perhaps rude
and imperfect, but it was a visual eye and had vast possibilities.
The animal is taking cognizance of ever more subtle elements in its
environment. 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. They transformed the annelid parapodia into legs and
developed wings. They attained life in the air. They devoted the
muscles of the body largely to the extremities and gained swift
locomotion. They have a fair circulatory and an excellent
respiratory system. Best of all, they developed a head and a brain
by fusing the three anterior ganglia of the body. The insect could
and does think. Such a structure ought to lead to great and high
results. But actually their possibilities were very limited. They
have not progressed markedly during the last geological period.
Their external skeleton was easily attained and brought speedy
advantages, which for a time placed them far above all competitors.
But it limited their size and length of life and opportunities, and
finally their intelligence. They remained largely the slaves of
instinct. They followed an attractive and exc