34^ Florence Peehl 



es 



appeared and the complete new anlage developed. If on the 

 other hand the two rows were separated later after they were well 

 defined, the first method of completion was followed. The prox- 

 imal piece is, therefore, as Driesch has shown, capable of com- 

 pleting itself in a distal direction. The small piece {A) bearing 

 the distal row of tentacles, is also able to complete itself distally, 

 but as far as I am aware no one has found that such a piece is 

 capable of forming new proximal tentacles, thus completing itself 

 in a proximal direction. 



It seemed to me worth while to repeat this experiment in order 

 to find out at what time the distal piece (Fig 20, A) becomes so 

 highly differentiated that it is no longer able to complete itself 

 proximally, and also to observe the other methods described by 

 Driesch, especially the "Auftheilungsmodus" which I had never 

 seen, although I had repeated the experiment more than a hundred 

 times. 



In order to find out the exact time when the small piece (Fig. 

 20yA) becomes too highly differentiated to complete itself, it was 

 necessary to remove the tip of the stem before the tentacle ridges 

 were visible. Driesch tried this on forty-five pieces, allowing 

 about twenty-four hours to intervene between the first and second 

 operations. Out of these forty-five pieces, thirty-seven developed 

 one row of tentacles, two formed a double row, and six a complete 

 hydranth without a stalk. Five of the six pieces that formed a 

 complete hydranth were "zu gross," therefore he considers that 

 there were only three out of forty which developed more than the 

 distal row. He concludes that there is therefore a definite time 

 before the anlage appears, when the character of the further 

 development of the smaller tip is determined. In order to deter- 

 mine the exact position of the tentacle ridges before they are visible 

 on the outside, it was necessary to measure a number of anlagen, 

 then to take the average length. Fifty pieces were cut from dif- 

 ferent stems, and left undisturbed until the anlage was visible on 

 each. Measurements were then made, first from the tip of the 

 stem to the base of the proximal tentacles (Fig. 21, P), and second 

 from the tip of the stem to the base of the distal tentacles (Fig. 21, 

 D) the average length of P was 1.7 mm. of Z) .6 mm. 



