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m e n t e d tract was produced. This has been done in figure 5, in 

 which the clotted line shows the relative frequency of the regeneration 

 of the given number of rings from 2 to 11, and the dot-and-dash line 

 the relative frequency of the different lengths of the stem when an 

 unsegmented tract was produced. It is plain from this figure, that 

 the occurrence of the secondary maximum is due to the fact that the 

 maximum of the curve of cases containing an unsegmented tract is 

 removed some distance from the maximum of the curves of cases con- 

 taining no unsegmented tract. There thus appear to be two distinct 

 forms about which the results group themselves — the form without 

 the unsegmented tract and that with it. The typical number of rings 

 for the first is from 3 to 7 ; for the second, 9 to 11. On each side 

 of these typical conditions there are scattering forms, but the sum of 

 the scattering cases of regeneration without unsegmented tract pro- 

 ducing more than 7 rings and those with unsegmented tract producing 

 less than nine rings results in a depression between the maxima pro- 

 duced by the typical conditions. 



6. I do not know why 3 — 4 rings predominate after a y cut, 

 instead of 6 rings as after an a or a ß cut. In connection with this 

 fact, however, it is necessary to state that in the y cut, two to three 

 rings of the distal segmented tract, on the average, remained behind 

 attached to the stem. It may very well be, however, that these facts 

 do not stand in the relation of cause and effect, but that the smaller 

 number of rings regenerated after a y cut may be merely an expression 

 of the general tendency for fewer rings to be produced after such 

 a cut. 



7. Regeneration takes place regularly in nature. I have examined 

 many cases, and counted the number of rings in the regenerated portion. 

 The planes of division seem to occur far more frequently just below 

 the hydrauth than elsewhere ; in fact, observations on the hydroids on 

 the rock-weed lead me to believe that the hydranths may be spontane- 

 ously lost when the conditions are unfavorable for the existence of the 

 hydroid, regeneration occurring upon return of favorable conditions. 

 While at Woods Holl in April 1893 at the end of a severe winter, I 

 found regeneration taking place at the distal end of most of the 

 hydroids, apparently just emerging from winter torpidity. The difference 

 in appearance between the old diatom-covered part of the stalk and 

 the newly-formed, enabled me to count the regenerated rings. In 

 100 cases counted, I found an unsegmented tract produced only once ; 

 there were 4 cases of 2 rings; 30 of 3 r., 47 of 4r., 15 of 5 r., and 

 1 each of 6 r., 7 r. and 9 r. The proportions are not very different 



