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This again is a sign that the muscles are becoming more important, for the excretory system is needed mainly to remove their waste. These tubes maybe only greatly enlarged glands of the skin. TURBELLARIAN. LANG. va and ha, front and rear branches of gastro-vascular cavity; ph, pharynx.
Now the turbellarian is small and sluggish, with a fair digestive system. With a great amount of nutriment at its disposal the reproductive system came rapidly to a high development, and relatively to other organs stands higher than it almost ever will again.
We must now try to discover how these potentialities became actualities in higher forms. The third stage in our ancestral series is the turbellarian. This is a little, flat, oval worm, varying greatly in size in different species, and found both in fresh and salt water. Some would deny that this worm belonged in our series at all.
The perivisceral cavity, formed perhaps by cutting off and enlarging the lateral pouches of the turbellarian digestive system, serves as a very simple but serviceable circulatory system.
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.