BY DR. R. VON LENDENFELD. 213 



colony would in consequence not be able to swim away whilst the 

 small embryo escaping the Gonongium could easily penetrate the 

 marine undergrowth, which, of course, in this case, is of 

 advantage to the colony, hiding and sheltering the Gonophore. 



I have, therefore, in doubtful cases, placed those Hydro- 

 medusinae, which have Gbnophores at the base of the colony 

 under the Hydropolypinae, those on the other hand, which bear 

 exposed Gonophores under the Hydromedusinae. 



The first suboi'der of the Hydromedusse, the Hydropolypinae, 

 comprises accordingly Hydi'a, the Clavidae, Eudench'idae, Cordy- 

 lophorinae, Bimei-ina?, Campanularinae, Sertularinae, the Plumu- 

 laridse, and Dicorynidae. I have also placed the Graptolithidae 

 under this heading. 



We meet with cpiite a different kind of Polymorphisne in 

 another series of Hydrornedusse. Here Medusas are formed, that 

 is Hydroid persons, which lead a free life and are provided with 

 an apparatus for free locomotion. This apparatus is in most cases 

 a bell-shaped Umbrella, an extremely clumsy and unsuitable 

 propelling organ. Only very few Medusae are destitute of an 

 Umbrella and crawl on their mai-ginal tentacles like Clavatella 

 (Eleutheria.) 



These Medusae, which had originally the function of distributing 

 the species like the winged Imagines of Insects, with which 

 they are to be compared, are small when born and often grow to a 

 large size afterwards. In such cases the nourishment assimilated 

 by the Medusa greatly exceeds that, which the Polyp colony 

 needs. Such Hydromedusae however (Zygodoctyla) are rare. In 

 most cases they remain small, losing more and more the function 

 of taking up noui-ishment which in such cases devolves on the 

 Polyp colonies. 



Finally Medusa? are produced which only live a short time 

 (Globiceps), and which already bear ripe sexual products at the 

 time of their liberation. The stomach of such Medusae may even be 

 obliterated (Eucopella) and an organism is produced, which like 

 the Ephemera is in fact only an apparatus for carrying the 

 sexual product to a greater distance like the Hectokotylus. 



