OF THE HYDROMEDUS^E. 415 



So far as I am aware, only one modern writer has advocated any other homology be- 

 tween the two forms than the one which I have stated. Ray Lankester has proposed (45) 

 to homologize the sub-umbrella of a hydromcdnsa with the stomadaeum of Anthozoa, 

 Ctenophora and other Metazoa, basing this view upon the improved and very improb- 

 able hypothesis that the young specimens of Limuoeodium which he: has described are 

 egg-emhryos. He does not state his view very clearly, but he must either believe that 

 those Metazoa which are furnished Avith a stomadaeum are the modified descendants of a 

 form like an adult medusa, or else he must believe that the young Limnocodium repre- 

 sents the ancestral condition of the medusae, and that the presence of a bell cavity is a 

 very old characteristic. If he intends to advocate the latter view, it is plain that he can- 

 not regard the medusa as an ordinary hydroid specialized for locomotion. 



Many authors who have fully recognized the close similarity between the hydra and 

 the medusa, and some who have been among the most important contributors to our 

 knowledge of the subject, have nevertheless held that a medusa is not ecpiivalent to a 

 single hydra, but to a polymorphic hydroid community; that a medusa is not a person 

 but a cormus. 



This view has long been a favorite one, and it appears in many forms in the literature 

 of the subject. The following extracts from my notes will serve to show how frequently 

 it has been advanced, although I do not believe that the writers quoted are all who 

 might be referred to. In 1854 W. Thompson compared the reproductive process of hy- 

 droids to that of plants and pointed out the resemblance between a medusa and a flower 

 (59), and in 1860 Jager (35) enlarged upon this familiar comparison and attempted to 

 show that the medusa bears the same relation to the hydroid colony that the flower does 

 to the plant, not only in position and in its reproductive function, but in its ultimate 

 morphological structure also. He says it is made up, like the flower, of several circlets 

 of individuals; that the tentacles, sense-organs, reproductive organs, etc., are all mor- 

 phological individuals; that the swim-bells of Siphonophores are sterile flowers; that the 

 medusa-buds of Hydractinia are flowers without calyces and that alternation of genera- 

 tions should more properly be called "antho genesis." 



In 1S5G Wright advanced the opinion (63) that a veiled medusa is to be compared with 

 a polymorphic hydroid community like Hydractinia, which he regards as a single person, 

 not a cormus; that the umbrella is homologous with the flat, spreading root of Hydrac- 

 tinia, its chymiferous tubes with the canals of the root; that the stomach of the medusa is 

 a nutritive hvdranth, its tentacles spiral zooids, its reproductive organs medusa-buds, etc. 



At a time when homology was not regarded as having any phylogenetic significance, 

 there was little check upon such fancies as those of Jager and Wright, but they are 

 clearly of little more scientific value than Morch's suggestion (53) that the Acalephs 

 should be placed with the Mollusca on account of the imaginary resemblance between 

 Lima and a medusa. 



In 1856, Leuckart (47) in his account of the structure of a Trachomedusa, Agalma 

 Peronii, figures and describes the reproductive organs. They form a circlet of eight 

 hollow-stalked pouches, within the walls of which the eggs are developed; while their 

 central chambers are outgrowths from the digestive cavity. The pouches are arranged 

 in a circle around the base of the pendent stomach, and he calls attention to the marked 



