North- American Freshwater Jellyfish. 131 



About two months after Mr. Bourne's discovery I first 

 detected Microhydra Byderi upon some stones collected the 

 previous autumn from the rocky bed of Tacony Creek, a 

 rapidly flowing mill-stream near Philadelphia, Pennsylvania, 

 a small affluent of the River Delaware, but far above tide- 

 level. Some peculiarities in its structure and mode of gemmi- 

 parous multiplication were described by my valued friend the 

 late Dr. John A. Ryder*. 



Dr. Ryder had not, at the time of writing the above paper, 

 seen the living organism which he there described. Speci- 

 mens werCj however, some years later placed in his hands for 

 study and watched for many months with exceeding interest. 

 His early death has left in the possession of his representatives 

 many excellent drawings and some valuable micro-slides as 

 the only evidences of his interest and labour. No descriptive 

 text has been found ; and the sorrow that his many friends 

 feel at his early removal has, to me, this added regret — that 

 he was not able to complete an investigation, which, not 

 unnaturally perhaps, I felt to be of so great importance, and 

 that he cannot now share with us our great delight in wit- 

 nessing the further development from Microhydra Ryderi of 

 a " medusiform adult stage." 



As may be seen by a comparison of the papers above 

 named, all of them preliminary and incomplete, there are 

 obvious points of resemblance as well as of difference between 

 these minute organisms that appeared, almost simultaneously, 

 at geographical points so widely distant. The supposition 

 that the form observed by Mr. Bourne is the earlier condition 

 of Limnocodium is, of course, greatly strengthened by my 

 actual observation of the budding and separation of free- 

 swimming Medusa from M. Ryderi f. 



We read that the specimens of Limnocodium often, perhaps 

 generally, disappeared from the tanks about the end of June 

 or July +. It is greatly to be regretted that the glass jars 

 containing my species were not carefully examined through- 

 out June and July of the present year, during which period 

 there may have been a larger production of maturing jelly- 

 fish. On the first day of August, however, my attention was 

 arrested by the spasmodic contraction of an evident Medusa in 

 the above-mentioned jar, and, during several following days, 

 Prof. E. P. Cheyney and myself, on frequent occasions, 

 watched the swelling buds upon colonies of Microhydra that 



* ' American Naturalist,' Extr., Dec. 1886, t). 1232 &c. 

 + This alternation and progression may nave been seen, later, in 

 England, but I shall have to plead ignorance of the fact. 



\ In one case " swarms " are reported Aug. 18, 1882, at Kew Gardens. 



