PHYLUM PLATYHELMINTHES 



ISI 



great amount of coloring matter in its body (Fig. 98, 2), but an 

 allied rlatworm, Dendroccelum lacteum (Fig. 98, 1), is cream- 

 colored, and its anatomy is more easily made out. 



!»-.' 



Fig. 97. — Planaria polychroa, a fresh-water llatworm. 1, eye; 2, side of 

 head; 3, proboscis; 4, pharynx sheath; 5, genital pore. (From Shipley and 

 MacBride.) 



Anatomy and Physiology. — External Features. - - Figure 

 97 shows the principal external features of a planarian. A pair 

 of eye-spots (1) are present on the 

 dorsal surface near the anterior end. 

 The mouth is in a peculiar position 

 near the middle of the ventral sur- 

 face. From it the muscular pro- 

 boscis (j) may extend. Posterior 

 to the mouth is a smaller opening, 

 the genital pore (5). The surface 

 of the body is covered with cilia 

 which propel the animal through 

 the water. This is not the only 

 method of locomotion, since mus- 

 cular contraction is also effective. 



Internal Anatomy and Physi- 

 ology. — A study of the structure 

 of the adult and of the early em- 

 bryonic stages shows Planaria to 

 be a triploblastic animal possessing 

 three germ-layers, ectoderm, meso- 

 derm, and entoderm, from which 



I 



Fig. 98. — Two species of 

 fresh water flat worms. 1, Den- 

 droccelum lacteum; 2, Planaria 



maculala. (From Davenport, 



several systems of organs have been after Woodworth.) 



