57^ Chas. W. Hargitt. 



monograph on "Fossil Medusae" Walcott^ has described a large 

 number of fossil medusae, among which several cases of remark- 

 able variation are recorded. In some the variation was so general 

 as to render difficult specific diagnosis. For example, in the 

 description of Brooksella alternata the author says: "The varia- 

 tion is so great in this species that a brief diagnosis is of little 

 value." . . . "The umbrella lobes vary in number from 

 6 to 20 or more, and in form from broad, slightly rounded to 

 narrow and strongly rounded. There is no regular sequence of 

 6, 8, 12, etc., on the contrary the irregular numbers 5 and 7 are 

 largely represented, and 6 and 8 are abundant." 



Again in his description of Laotiara cambria he says: "Its 

 variations are greater than in Brooksella." The lobation of the 

 exumbrella is from the simple four-lobed variety, through series 

 of 5, 6, 7, to 8 or more, to what he designates as the compound 

 type, which are apparently medusae in process of fission. In this 

 species, as in the preceding, there seems to be no definite regularity 

 or sequence in numerical order. In the words of the author: 

 "In many individuals there is no regularity, and in the extreme 

 forms there is an irregular network of subumbrella lobes and 

 oral arms." 



From the numerous figures of this well-illustrated monograph 

 it is quite evident that similar, if not equally extensive variation 

 is also present in many other of the species described. It is not, 

 however, within the scope of this paper to undertake an extensive 

 review of the entire subject, and hence further details concerning 

 this phase will not be submitted. Citation of the foregoing facts 

 may serve to direct attention of those interested to a phase of the 

 general problem hitherto little considered. 



INFLUENCE OF ENVIRONMENT ON VARIATION. 



As is well known, there is a more or less currently accepted 

 belief in the influence of environment as a modifying factor in the 

 variation of organisms. Reference has already been made to 

 Haeckel's views as to the influence of such factors in relation to 

 the abnormalities arising in medusae feared under artificial con- 

 ditions, and to his further suggestions concerning the probable 

 influences of similar conditions in nature. 



'Mono. Unit. States Geol. Surv., vol. xxx, Wash., li 



