PHYLUM PLATYHELMTNTIIES 



155 



Hon occurs, and cocoons are formed, each containing from four 

 to more than twenty eggs, surrounded by several hundred yolk 

 cells. The development of the egg is illustrated and explained 

 in Figure 101. 



Regeneration. — Planarians show remarkable powers of re- 

 generation. If an individual is cut in two (Fig. 102, A), the an- 

 terior end will re- 

 generate a new tail 

 (B, B 1 ), while the 

 posterior part de- 

 velops a new head 

 (C, C 1 )- A cross- 

 piece (D) will re- 

 generate both a 

 head at the anterior 

 end, and a new tail 

 at the posterior end 

 (D'-D*). The head 

 alone of a planarian 

 will grow into an 



entire animal ^-C, - p> IG IQ2 — Regeneration of Planaria maculata. 



E 3 ). Pieces CUt A, normal worm. B, B 1 , regeneration of anterior 



r . half. C, C 1 , regeneration of posterior half. D, cross- 



irom various parts piece of worm j)i, D 2 , D 3 , D 4 , regeneration of same, 



of the body will E, old head. E 1 , E 2 , E 3 , regeneration of same. 



, F, F 1 , regeneration of new head on posterior end of 



alSO regenerate old head (From Morgan.) 



completely. No 



difficulty is experienced in grafting pieces from one animal 

 upon another, and many curious monsters have been produced 

 in this way. 



2. Class I. Turbellaria 



The Turbellaria (the class to which Planaria belongs) are 

 free-living Platyhelminthes with ciliated epidermis. Special 

 ectodermal cells secrete mucus or produce rod-like bodies called 

 " rhabdites." 



