360 GENERAL BIOLOGY 



Study 42. Experiments with regeneration in planarians. 



Materials needed: Plenty of living planarians, in indi- 

 vidual dishes of clean water. This is a running experiment, 

 requiring repeated observations at successive laboratory 

 periods. 



Cut small pieces from some of them, cut others in two in 

 the middle, at various planes, and make diagonal clefts in 

 others to observe polarity of the partly severed pieces. 



Divide the bodies of a number of the animals. They 

 may be cut with fine and sharp scissors while creeping, fully 

 extended, on a piece of thin wet paper; cut paper and 

 planarian together, at single rapid but careful strokes. 

 Excessive cutting up of the animals may be avoided by 

 apportioning the work among several members of the class. 

 (That need not be a serious consideration, however, since 

 the regenerated pieces may be returned to the waters 

 whence the whole ones were originally taken, and the tribe 

 will have been increased by the operation) . 



The record of this study should consist of sketches of the 

 animal, one for each operation, and outline drawings of the 

 forms assumed at subsequent examinations. 



Grafting. The parts of two organisms, if brought 

 together by clean cut surfaces, with growing parts apposed, 

 and held in close contact for a time, may grow together, 

 and, if complemental parts be taken, they will thereafter 

 function as a single organism. This is grafting. In the 

 higher plants, on which it is most commonly practiced, the 

 piece that is to represent the top of the combined plant 

 is called the don, the rooting piece is called the stock. 

 These two parts are combined into one in a number 

 of well known ways, three of which are represented in 

 figure 210. The essential things in the practice (with 

 such woody plants as these shown) are i) the bringing of 



