Regeneration in Rhizostoma Piilmo. 89 



It would seem, therefore, that in the light of these facts one 

 may well question the validity of Uexkiill's conclusions, or rather 

 inferences. The mere presence of whitish blotches on an organism 

 would hardly justify, without the most conclusive demonstration, 

 the inference that the presence of similar effects produced by some 

 reagent proved them identical or even analogous. That there 

 may have been certain pathologic conditions operating upon these 

 medusae of which the whitish blotches were in some respects ex- 

 pressions may have some measure of probability. But that these 

 blotches were in themselves the inciting stimuli giving rise to the 

 simulated rhythm must be regarded as doubtful, if not indeed, 

 highly improbable. Such a conclusion could hardly have been 

 suggested had it been observed that the same whitish blotches are 

 not unusual on specimens which have been for some time in 

 aquaria. Moreover, their presence on such specimens has not in 

 the least, so far as my own observations have gone, served to 

 Introduce any variation of the normal rhythm, a condition which 

 might not be unusual on the assumption of these disease patches 

 becoming sources of abnormal stimuli, and thereby Introducing 

 erratic or conflicting factors into the physiological processes of 

 the organism. It Is well that attention should be directed to 

 disturbing conditions of this character in order that undue weight 

 be not given to a single factor in determining so Important a prob- 

 lem. On the other hand It may be quite as Important that In 

 discrediting one conclusion there Is not substituted another of 

 even less value. 



One might be tempted in this connection to go somewhat out 

 of the way to consider Uexkiill's conclusions as to the purely 

 mechanical function of the rhopalia In relation to the rhythmic 

 action of the umbrella of medusae. If they might be supposed to 

 act after the fashion of the clapper of a bell, using his figure of 

 comparison, In the case of such medusae as Rhizostoma what ex- 

 planation shall we have for the Identical rhythm exhibited by 

 many other medusae entirely devoid of rhopalia or any equivalent 

 organ? Many other objections will immediately arise when one 

 reflects upon the very different histological conditions of structure 

 found in these organs in various medusae, but to take up any one 



