188 C. M. CHILD. 



that of posterior new tissue decreases. The development of the 

 new head is more rapid in anterior than in posterior pieces. The 

 position of the new pharynx is posterior to the middle in anterior 

 and anterior to the middle in posterior pieces. Short pieces 

 from the extreme anterior region frequently fail to develop a 

 new posterior end. Fig. 2 shows a piece of this kind. Figs. 3, 

 4 and 5 show three pieces, the first from the anterior, the second 

 from the middle and the third from the posterior region. The 

 different amounts of new tissue produced are seen in the figures. 

 All these graded differences, like those in Planaria dorotocephala 

 (Child, 'lie), indicate the existence of a physiological gradient 

 of some sort along the axis. As a matter of fact this gradient is 

 essentially similar to that which exists in P. dorotocephala (Child, 



'12, 



2. The Encystment of Artificially Isolated Pieces in Relation to 

 Size of Piece and Region of Body. 



Pieces isolated by section may undergo the regulation to whole 

 animals either with or without encystment. The frequency of 

 encystment varies with region of the body from which the piece 

 is taken, with the size of the piece and with the physiological 

 age of the animal. The following records of series will serve to 

 illustrate this. In these series a number of worms, ten, twenty 

 or twenty-five, from the same stock and as nearly as possible of 

 the same size and in the same physiological condition are cut 

 into a number of as nearly as possible equal pieces, the corre- 

 sponding pieces are placed together in one lot and results recorded 

 for each piece. Since different numbers of worms are used in 

 different series the results are given in percentages. 



Series ip, April ij, IQII. Ten worms, full grown (12-14 

 mm.), but still feeding and deeply pigmented. Heads removed 

 and remainder of body cut into two equal pieces, a, the anterior, 

 and b, the posterior. Table III. show's the percentages of the 

 pieces which develop into whole worms without encystment 

 and of pieces which encyst soon after the operation and emerge, 

 from a few days to several weeks later, as whole worms after 

 regulation in the cysts. 



