No. 5-] VARIATION AMONG HYDROMEDUSAE. 227 



explained as due to distortion caused by the pressure of the 

 ova within the bell. This I am convinced is a mistaken virw, 

 for I have noted it upon specimens both living and on those 

 killed and preserved in formalin, in specimens with and with- 

 out eggs. It seems, moreover, to be wholly restricted to the 

 outer ectoderm only, in no case involving the inner ectoderm of 

 the subumbrella. There is nothing indicative of the cause or 

 character of these excrescences. Whether they are permanent 

 or merely transient features I am not able to say, the short- 

 lived condition rendering any determination difficult if not 

 impossible. 



Ncmopsis. 



Through the courtesy of Mr. Strong I had the privilege 

 of examining a small collection of about one hundred speci- 

 mens of Nemopsis Bachei taken in the tow off Tarpaulin 

 Cove. The variations here seemed quite as evident as in 

 Eucope and Gonionemus. Here again the variable features 

 included radial canals, manubrium, gonads, and tentacles. 

 Fully five per cent showed some feature of variation. About 

 two per cent had but three radials and three gonads. One of 

 these showed a definite correlation, including all the organs 

 named above. One, however, of the trimerous forms had a 

 fourth sensory bulb and tentacles, though these were less 

 prominent than were the other three sets. The oral tenta- 

 cles likewise shared in the correlation. 



One specimen was a symmetrically pentamerous form with 

 a perfect correlation of all the organs under consideration. 

 Another specimen was quite as symmetrically hexamerous. 



Several other specimens exhibited apparent symmetry in the 

 number of gonads. Frequently one of the series showed the 

 gonad of one canal very unequally developed as compared 

 with the others. But while approaching sexual maturity, and 

 in many cases fully so, it is of course impossible to say with 

 certainty that the short gonad might not have shown further 

 development with age. In any case it certainly showed varia- 

 tion as to development. 



