Regeneration in Rhizostoma Puhno. 85 



slightest evidence of any deviation from the exact position occu- 

 pied by the original organ. 



The apparent exceptions referred to are as follows : First, that 

 in at least two cases twin rhopalia were developed instead of the 

 single original one which had been excised. This is well shown in 

 Figure 3. Second, that in one case two rhopalia were regenerated 

 instead of the one originally excised, but unlike the preceding, 

 they appeared at different points — one in the usual position at 

 the upper angle of the notch, the other at the lower, or marginal 

 portion of the notch, as shown in Figure 4. 



The mere fact of the occurrence of double rhopalia during re- 

 generation instead of single ones is not of itself particularly re- 

 markable, for the occurrence of such features is not an unusual 

 one in a state of nature, both ephyrae and adult medusae being 

 occasionally found with such double organs. Some further in- 

 quiry should, however, be directed to the peculiar position in 

 which the organ noted in Figure 4, at a, occurs, namely, at one 

 side of the notch and near the margin instead of the usual posi- 

 tion. On the assumption that these organs are of sensory func- 

 tion and correlated with marginal nerve centers it might be 



a' 



Fig. 4. 

 Two regenerated rhopalia; a, near the margin. 



thought that in regeneration they would be likely to occur in close 

 relation with such centers, and that the case under consideration 

 might be thus explained. The fact is very clear, however, that such 

 is not the case with the vast majority of the experiments where ap- 

 parently the relation of nerve centers had nothing whatever to do 

 with their position in regeneration. And when furthermore we 

 reflect that these are not nervous organs in any true sense, either 

 in their origin or development, though possibly correlated with 



