OF THE IIYDKOMEDUSiE. 425 



In his paper on Tetrapteron (16) he says that he has expressed his view of the man- 

 ner in which alternation originated among the medusae in his paper on Halistemma 

 (15), but I am unable to find it there, or to find any statement of his view earlier than 

 1880. 



A recent writer in Nature (28) states, p. 69, that Clans supports the view originally 

 formulated by Leuckart, that alternation of generations has originated among the me- 

 dusae through polymorphism, rather than through a modification of metamorphosis, but 

 he gives no references in support of his statement, which is probably an error like many 

 others which occur in the paper. 



In 1883 I published a paper in which I gave a very brief explanation of the origin of 

 alternation iii the medusae. My view is identical with that which I have quoted from 

 Clans, although I reached it independently and in ignorance of Bohm's and Glaus' writ- 

 ings on the subject. The paper is a short abstract without illustrations, but my conclu- 

 sion was based upon the life-history of the Narcomedusae and Trachomedusae, which 

 seem to me to furnish much more conclusive proof than any which these writers bring 

 forward. 



The statement is as follows : " It is hardly possible that the form of development which 

 we now find in most of the Hydromedusse can bear any close resemblance to their prim- 

 itive life-history, and there are many reasons for believing that alternation of genera- 

 tions has gradually arisen through the modification of c metamorphosis.' In Cunina we 

 seem to have the ancestral form of development: a direct metamorphosis without alter- 

 nation * * * The larva of Cunina is a hydra with the power of asexual multiplication; 

 but, instead of giving rise to medusa-buds, like an ordinary hydroid, it becomes directly 

 converted into a medusa by a process of metamorphosis: it is a true larva and not an 

 asexual generation, although the occurrence of asexual reproduction renders the gap be- 

 tween this form of development and true alternation very slight indeed. 



In Cunina we have a series of this kind: 



Vgg 



I 

 Larva - Larva - Larva 



I I I 



Adult Adult Adult 



If the larva which is produced from the egg were to remain permanently in the hydra 



stage we should have a series like this 



Egg 



Hydra - Hydra - Hydra 



Medusa - Medusa 

 and such a history would be a true alternation." (12). 



A few months later, March 1881, Fewkes published a paper (19) in which he says 

 " That exceptional form of development, called alternation of generations, which exists 

 in the fixed hydroids may be regarded as the irregular not the normal method. It is an 

 adaptation resulting from peculiar circumstances and a departure from a rule in one di- 



