293 



from those of regeneration in glass vessels, and serve to indicate the 

 non-pathological nature of the latter results. 



8. A cause of variation in that which is produced by a cut at 

 any level appears to exist in the conditions of food — especially 

 oxygen -supply. As is well-known, hydroids in stagnant water produce 

 stolons in place of hydranths, and I have already alluded to the fact 

 that a smaller proportion of hydroids regenerated after any cut when 

 the water in which they were developing stood unchanged. I have 

 found, that when a small proportion of hydroids regenerated, and many 

 stolons in place of hydranths were produced — indicating unfavorable 

 conditions in the water — the average number of rings regenerated 

 after a cut at any level diminished, sometimes as much as 25°/ . 



V. Conclusions. 



First. The regenerative tissue is not differentiated 

 at different levels to produce different things, in- 

 dependent of environment; but on the contrary, the 

 embryonic tissue at all levels may produce te same 

 things. 



Second. Wholly aside from the necessary production of definite 

 things, there may be acquired in certain embryonic tissues a usual 

 method of development, independent of environment. 



Thus we find (compare figure 6) that in Obelia after the y cut, the 

 middle 70 °/ (from 15 °/ to 85 °/ ) of the cases (as shown by the curves 

 of distribution of regeneration) are distributed between 2 rings and 5 rings 

 — a range of 3 rings. 



This usualness in the result of development is not a character of 

 the germ-plasm at all levels. 



In Obelia, after a ß cut, the middle 70 °/ of the cases is distributed 

 between 4 rings and 10 rings — a range of 6 rings, and after an a cut 

 between 5 rings and 13 rings — a range of 8 rings. 



The definiteness of the result is in Obelia a function of the distance 

 of the cut edge from the base of the stem. This fact is correlated 

 with a second, that the proportion of cut hydroids which regenerated 

 after cutting was greater the more distal the cut; and this with still 

 a third, that, in nature, regeneration takes place more frequently from 

 the more distal than from the more proximal levels. Thus the 

 resorption and regeneration of the hydranths at the distal end of 

 the stem recurs so constantly in the stock that one is almost forced 

 to conclude that we have here to do with a physiological process, 

 comparable with the continual resorption and regeneration of the polyps 

 of marine Bryozoa. The hydranth, together, with one or two of the 



