FLAT WORMS 



37 



habits and experiences of the animal. Headless forms respond to 

 light but less quickly. As a rule if the head and eyes of a planarian 

 are removed the headless portion reacts as before but much more 

 slowly. In marine flatworms where the ganglia are more concen- 

 trated in the head region and where there are fewer ganglion ceils 

 along the lateral cords, the activities of the headless worms are 

 much less perfect than in planarian worms of fresh water. 



In the flatworms special cells of the ectoderm give rise to the 

 head ganglia. Later stages, or the development of the peipheral 

 svstem have been but little studied. 



Fig'. 9. Nervous system of polyclad and triclad worms. A. Snycoelidium, 

 Wheeler. B, C. Head and tail ends of Sorocelis, Seidl. D. Brain and 

 head end of Pla)iaria bohmegi, Weiss. E. Planaria apitia, Micholetzky. 

 F and H. Eyes of Planarians, Hesse. I, J. Nerve endings in skin 

 Planarians after Monti. K. Brain and eyes of Lcptoplana, Schmidt. 

 L. Nervous system and eyes polycladid, Lang. 



Kepner and Rich, 1918. have studied the reactions of the pro- 

 boscis of flatworms. In accordance with Monti, '97, and Steiner, 

 '98, they found that the ventral nerves are ganglionic and these 

 centers exercise control over the posterior parts of the body. The 

 middle branch from each of these ventral nerve trunks leaves the 

 ganglion that lies nearest the base of the proboscis and from here 

 enters it. When the proboscis is removed from the animal it 

 undergoes autoamputation. Without the control of the adjacent 



