1902.] NATURAL SCIENCES OF PHILADELPHIA. 773 



more than would be swept out of the shallow water by the tide. 

 Not only these considerations, but all the other indications seem to 

 point to a direct transformation of the polyp to the adult gonosome 

 without leaving the eel-pond. The habit of the polyp of resting 

 with tentacles extended and adhering to the bottom, the feeding 

 reactions, the form of coelenteron, manubrium and oral opening, 

 the manner of origin of the tentacles, all resemble the correspond- 

 ing conditions in the adult so closely that it is easy to regard this as 

 the most likely theory. May it not be that the same type of 

 metamorphosis as that which takes place in Liriope (Brooks, 1895) 

 is passed through in this genus as well ? In Liriope the coelente- 

 ron is transformed into the system of chimiferous tubules by the 

 growth of fusion areas which unite the upper and lower walls of 

 the cavity, except where they are to be left separate along the lines 

 of the canals. PI. XXXII, fig. 18, is a camera drawing of a 

 twelve-tentacled gonosome of Gonionema, which has very much 

 the appearance of the newly metamorphosed Liriope}^ The trans- 

 formations which are necessary to bring about the adult from the 

 larval form are a change in the coelenteron to a system of tubes; 

 the centralizing of the diffuse nervous system to form the two 

 nerve-rings; the appearance of new tentacles provided with adhe- 

 sive disks, and of tentacles modified to the form of sense-organs, 

 from the expanded tentacular ring; and the growth of the velum. 

 The relative size of the fully developed polyp and the youngest 

 medusa offers no contradiction to such a conception of direct meta- 

 morphosis; if the polyp grows as rapidly in ihe natural environ- 

 ment of the eel-pond as in the laboratory, even allowing for a long 

 period of absolute quiescence during the cold weather, the discrep- 

 ancy in size is easily accounted for. 



Youngest Medus.e — Arrangement of Tentacles and 

 Sense-Organs. 



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

 mens of Gonionema were taken in a tow net at the surface of the 

 eel-pond. Several of these had sixteen tentacles, some had twelve, 

 one had only eight. A careful study of these very young and 

 evidently recently metamorphosed gonosomes has brought out some 

 exceedingly interesting points. 



" Brooks, 1895, PI. 41 ; Haeckel, Die Russelquallen, PI. 12. 



