MEDUSAE OF THE WORLD. 



Many of the medusae are modified more or less profoundly by environmental 

 conditions, and this gives rise to numerous local races, the determination of the 

 relationships between which is all but impossible in the present state of our knowl- 

 edge. Experimental work in this field is in its infancy, yet the few observations of 

 Hallez on Bongainvillia and of Browne in his experiments in maintaining various 

 hydroids under different conditions in aquaria suggest that the results of more 

 extended studies will be of great benefit to the systematist in determining the 

 natural limitations of species. A striking example of the profound effect of environ- 

 mental changes is seen in the experiments of Goldfarb, 1906, upon Eudendrium, 

 wherein he showed that after the regenerative process had entirely ceased in the 

 dark, it could be recalled into activity by an exposure of only five seconds to the 

 daylight. 



At present the natural classification of the species of such genera as Obclia, 

 Phialidnnn, Etttnna, Bougamvillia, etc., is impossible, and the Linnean system is 

 inadequate to the task of expressing their actual relationships. Indeed, with the 

 exception of the sponges and corals, there is no phylum of the animal kingdom more 

 difficult to classify than the medusae. 



In a work of this magnitude there must needs be both errors and omissions, 

 and for these I can but present my apologies in advance of their discovery, trusting 

 that all such will soon be discovered and announced, and that science may be more 

 advanced than hindered through the publication of this book. I trust that none 

 of my esteemed contemporaries will feel aggrieved at such criticisms of their labors 

 as may appear in the following pages, for should anyone find cause for such offense, 

 he may console himself in the fact that I am obliged to confess to having found 

 more to criticize and amend in my own previously-published papers than in those 

 of any other living naturalist. 



