THE ASEXUAL CYCLE OF PLANARIA VELATA IN 

 RELATION TO SENESCENCE AND REJU- 

 VENESCENCE. 



C. M. CHILD. 



I. THE LIFE CYCLE UNDER NATURAL CONDITIONS. 



During early spring in the region about Chicago, a planarian 

 appears in temporary ditches and pools, particularly in those 

 which are more or less filled with dead leaves. It is also often 

 found in permanent bodies of water such as springs, permanent 

 ponds and brooks, but seems to attain the greatest numbers 

 in the temporary ditches and pools. The animal is apparently 

 the species recently described by Stringer ('09) and named 

 Planaria velata. The shape and proportions of the larger 

 individuals are indicated in Fig. i. 



When the animals first appear soon after the ice melts they 

 are mostly only 2-3 mm. in length and commonly light in color. 

 They grow rapidly and soon the dorsal surface becomes very 

 deeply pigmented so that they appear almost black. They are 

 very active and their locomotion is much more rapid than that 

 of most other fresh water planarians. During this period they 

 react readily to meat of various kinds and can be collected in 

 large numbers by placing pieces of meat in the water. In about 

 four weeks they attain a length of 12-15 mm., their movements 

 gradually become slower, they cease to react to food, become 

 light gray in color from loss of pigment and sooner or later the 

 pharynx disintegrates. 



Within a few days after these changes a process of division 

 begins. As the worms creep about, the extreme posterior end 

 adheres to the substratum and the rest of the animal pulls away 

 and leaves it behind as a small fragment which becomes more or 

 less spherical and within a few moments is covered with a slime 

 which adheres to the underlying surface and hardens into a 

 cyst. This process of division is repeated, often several times 

 within a few moments, so that as the animal moves across the 



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