42 



metamorphosis; if the polyp grows as rapidly in the natural 

 environment of the eel pond as in the laboratory, even al- 

 lowing a long period of absolute quiesence during the cold 

 weather, the discrepancy in size is easily accounted for. 



X, YOUNGEST MEDUSAE , - Arrangement of Tentacles and 

 and Sense-Organs. 



During the last of June, 1900, a number of very 

 small specimens of Gonionema were taken in a tow-net at the 

 surface of tlie eel pond. Several of these had sixteen ten- 

 tacles, some had twelve, one had only eight. A careful 

 study of these very young and evidently recently metamor- 

 phosed gonosomes has brought out some exceedingly interest- 

 ing points, 



Hargitt (1901), in his paper on "Variations among 

 Hydromedusae" , discusses the arrangement of tentacles in 

 Gonionema; he approaches the qitestion as a student of vari- 

 ations, and unfortunately lacks the young material from 

 which I have found it possible to educe very definite rules 

 in the arrangement of marginal organs, and their order of 

 appearance. As a natiiral result Hargitt forms the conclu- 

 sion that so much irregularity occurs as to render it im- 



