Metagenesis among the Hydromedusce. 



29 



It is very probable that future research will show that even 

 this complex diagram is too simple for some of the Hydro- 

 medusae, and that there is, in some cases, a secondary alter- 

 nation between the first generation of free medusaj and those 

 which are produced by budding from this generation. The 

 life-history of these proliferous medusae has not been studied 

 as they are seldom found near laboratories and appliances for 

 research ; but there is reason to suspect that in some of them 

 only the medusjfi which are budded from the bodies of the 

 medusEe of the first generation become sexually mature ; and 

 if future research should prove this, we should have still 

 another alternation between the asexual proliferous medusa? 

 and these sexual descendants. 



In Hydractinia, the cormi of which are so similar to those 

 of Podocoryne that a drawing of one will correctly represent 

 the other, the life-history begins to simplify itself by the 

 degradation of the sexual medusai into sessile buds or repro- 

 ductive organs, which, however, still retain traces of their 

 former independent locomotor existence, traces which have 

 almost totally disappeared in Eudendrium and in many of the 

 Campanularians. 



The life-history of Uydractinia may be represented as 

 follows : — 



f ^ ( Nutritive Hydra 



Nutritive Hydra X \ Blastostyle x 



( Defensive Hydra 



IX. Hydractinia : _ I Nutritive Hydra 



Egg =Planula = Root X-^ Nutritive HydraX I Blastostyle X 



{ Defensive Hydra 



Nutritive Hydra X 



L 



Nutritive Hydra 

 Blastostyle X 



Defensive Hydra 



3Iedusa Bud<:Hggs. 

 Medusa Bud<zEggs. 

 Medusa Bud-^cEggs. 

 Medusa Bud<iEggs. 

 Medusa Bud<:Eggs. 

 Medusa Bud<:.Eggs, 



Now what is the significance of this remarkable series of 

 life-histories ? Most of the facts have long been known • but 

 the most conflicting interpretations of them have been ad- 

 vanced, and the student who seeks in the various monoo-rapjis 

 upon the subject an exposition of the relation between the 

 direct development of a single adult from each Q^g, which is 

 characteristic of most animals, and the circuitous historv 

 which is so remarkably exhibited by the medusas, will find "a 

 speculative literature which is almost unlimited, but a total 

 lack of agreement as to the true solution of this, the most 

 interesting of all the problems involved in the life of these 

 most interesting animals. 



