Variations Among ScyphomeduscB. 



sss 



A study of the table will naturally give rise to the question as to 

 how the several variations in these marginal organs are to be 

 explained. For example it will be observed that twenty-three 

 specimens had more rhopalia than marginal lobes. A reference 

 to Figs. I to 3 will quickly afford an explanation of this phenome- 

 non. The figures also show double and twin rhopalia, several 

 cases of which were found. Similar cases are cited by Browne 

 (op. cit.y p. 90), and in connection with their discussion he ven- 

 tures the suggestion that perhaps in later development and during 

 metamorphosis, by a growth of the margin these so-called twin 

 rhopalia may become separated thus giving rise to an independent 

 lobe. This seems to me to be extremely doubtful. As a matter 

 of fact it is well known that during growth following metamor- 



Fig. I. Diagram of marginal lobe showing twin rhopalia. 



Fig. 2. Compound marginal lobe, one of which contains twin rhopalia. 



Fig. 3. Compound marginal lobes the central one notched at the tip. 



phosis, increase of the marginal dimension takes place entirely 

 by growth of the inter-rhopalial areas. This is very easily seen 

 by a study of the appearance of new marginal tentacles and by 

 the origin and multiplication of the branching canals. It may 

 therefore be accepted as practically certain that the twin rhopalia 

 of the ephyra continue such in the adult medusa. It is also 

 almost certain that a similar condition is involved in the case of 

 such double rhopalia as are shown in Figs. 3 and 4. In these 

 respects, as in others, as cited by Haeckel (op. cit.) we may, I 

 believe, regard it as undoubtedly true that the larval variations are 

 carried over into the adult through the several phases of meta- 

 morphosis. Furthermore, this view is confirmed by the facts 

 clearly established, that the ratio of variation found in the adults 

 is essentially the same as that found m the ephyrae. 



