246 Chas. W. and G. T. Hargitt. 



In the earlier account by the senior author (op. cit.), it was 

 shown that the planulse might have variable life histories. It 

 should be noted that these observations were made under the 

 artificial conditions of the laboratory, and hence the variations 

 might be due to the more or less artificial conditions. The same 

 may also be said as to the scyphistoma. 



Encystment. — This is a condition often common where develop- 

 ment is limited to the laboratory. Attention was called to this 

 in the earlier account. Figures 38-40 show the aspect of young 

 polyps just emerging from the cysts, which in these cases become 

 floats, by means of which the polyps may be borne for some time. 

 Whether such a condition ever occurs in nature we have no means 

 of knowing, but so far as recalled it has not been made a matter 

 of record. All the observations point to the conclusion that the 

 phenomena associated with encystment are expressions of adapta- 

 tion due to unfavorable conditions of environment; and this may 

 serve to reconcile certain more or less conflicting accounts of 

 earher observers, more especially those of McMurrich (1891), 

 and Hyde (1894). 



The Scyphistoma 



Concerning this phase the earlier work of L. Agassiz was per- 

 haps the best of his entire account. Many of his admirable figs, 

 (cf. op. cit. pi. xi), of both Aurelia and Cyanea would illustrate 

 our own results quite fully. 



The account here given relates almost exclusively to Cyanea, 

 though scyphistomai of Aurelia have been kept under observation 

 at several times during the progress of these studies. As in the 

 life history of the planula, so in that of the polyp there is much 

 variability. In a small proportion of specimens there was a 

 metamorphosis into the ephyra within a period of about twenty 

 days after the planula attached itself. In the larger number the 

 period was much greater than this, thirty to forty days under 

 average aquarium conditions, while in some cases there was no 

 transformation even at the end of two months. In the case of 

 Aurelia the polyp life is apparently much greater, usually several 



