250 HARGITT. [Vol.. II. 



3. Variation among Hydromedusae appears to be much less 

 symmetrical and less definitely correlated than among Scypho- 

 medusae. 



4. Many phases of variation seem to be wholly devoid of 

 any adaptive features or tendencies. 



5. The ratio of variation is higher among the tentacles than 

 among other organs, and in many species higher than in all 

 other organs combined, - - a feature which is perhaps the most 

 conspicuous case of adaptation apparent in the entire series. 



Among the earliest references to variation in Coelenterates 

 is that of Ehrenberg ('37) relative to variation in Aurelia. 

 Later, Romanes ('74-'76) took up the subject with much more 

 detail, giving an extended account of the nature and extent of 

 variation, particularly in Aurelia, in which he figures and 

 describes many " monstrous forms of medusae " and points 

 out interesting correlations of radial canals, gonads, tenta- 

 cles, etc. 



Within recent times these observations have been much 

 extended, notably by Brown ('94), who distinguished more than 

 two per cent. 



Sorby ('94), Herdman ('94), and Unthank ('94) have each 

 recorded many interesting facts of variation in this medusa. 



In 1895 Brown still further extended his observations upon 

 Aurelia, and in connection therewith undertook a comparison 

 of a large number of the Ephyrae. He was able to distinguish 

 no less than 22.6 per cent of numerical variation in tentaculo- 

 cysts, a ratio very close to that earlier determined for adult 

 Aurelia. The observations seemed to show upon the whole 

 a tendency toward an increase in meristic characters. 



Ballowitz ('98) records extended observations upon Aurelia, 

 specially with reference to the gonads. While in general there 

 was more or less correlation in the numerical variation of these 

 organs with the actinal lobes, it was apparently less constant 

 than had been claimed by earlier observers. The highest 

 number noted was seven, while three was the minimal number. 

 One specimen in particular, which he names Ephyra abnor- 

 mitat, seems to be an unusual monstrosity, having a very large 

 balloon-shaped body with a correspondingly large manubrium. 



