99 



Fig. 27. all the sets except the first having the same 



number of tentacles. For figures of the adult, 

 see Agassiz (L), Mem. American Academy, 

 Vol. IV. p. 289; and McCrady, Proc. Elliot 

 Soc, Plate 10, under the name of Nemopsis 

 Gibhesii. In Lizzia, where there are secondary 

 clusters of tentacles between the chymiferous 

 tubes, the development is not isochronous in the 

 tentacles in the prolongation of the chymiferous 

 tubes and those between them. It is particu- 

 larly easy to trace the order of succession of 

 the different sets of tentacles in Lizzia, as the 

 MedusfB buds are formed on the probos- 

 cis, and develop with great rapidity ; from 

 YoMug Nemopsi.-:JJachei. these young MedusiB, in their turn, buds are 

 formed which become free Medusae in three or four days ; so 

 that in the course of a week there may be as many as three 

 successive generations swimming in a jar, which, a short time be- 

 fore, contained but a single Medusa. I at first supposed that the 

 young specimens of Lizzia, which I found subsequently in my jars, 

 had escaped my attention ; but I became satisfied that this was not 

 the case by isolating several specimens of our Lizzia with buds on the 

 proboscis, for on examining them, at frequent intervals, I saw the buds 

 upon their proboscis rapidly enlarge, and a few days afterwards I in- 

 variably found five or six free Lizzice nearly as large as the one which 

 had been isolated at first. The same experiment was repeated with 

 this Medusas which had thus been developed ; they were isolated with 

 the same result. 



In the young buds of our Lizzia, Lizzia grata A. Ag., there are at first 

 four large patches of pigment cells in the prolongation of the chymifer- 

 ous tubes ; the intermediate clusters then make their appearance. The 

 tentacles in the prolongation of the chymiferous tubes are first de- 

 veloped. We have one long tentacle for ^j^ 

 each tube. Soon afterwards the intermediate 

 tentacles are formed, one tentacle between 

 every two chymiferous tubes ; next a pair 

 of tentacles makes its appearance, one on 

 each side of the long tentacle in the pro- 

 longation of the tubes ; the next set consists 

 of a similar pair for the intermediate tenta- 

 cle ; when the tentacles of the young Lizzia 

 assume the appearance of fig. 28. In this 

 state they remain apparently until all the ten- 

 tacles have become equally developed. This is the appearance of most 



Youugr Lizzia. 



