TIBIA FORMOSA. 



115 



capsules along the circular tube, and yet these Medusae have all been 

 traced to a Campanularian-hke Hydrarium. Tuna differs from the 

 other genera just mentioned, in developing eventually these marginal 

 capsules, which are always wanting, at least in the shape of capsules 

 with limestone concretions, in the above-mentioned genera. See the 

 magnified portion of the circular tube of Tima (Fig. 168), and compare 

 this, crowded with marginal capsules, to the circular tube jig 1,1. 



of Melicertum and Lafoea. Havmg kept in confinement 

 males and females of this species, I succeeded in raising 

 from the eggs the Planula, and ultimately the Hydra- 

 rium, as in the case of Melicertum, where further details 

 will be found concerning the mode of development of 

 the Planula into the Hydrarium ; as this is identical in 

 both, I shall only describe the Planula and Hydrarium 

 as far as they differ from those of the Melicertum. 



The Planula is more pear-shaped {p, Fig. 171) than 

 that of the Melicertum, and takes a far greater elongation before at- 

 taching itself {p, Fig. 171.) The Hydrarium is also more slender, 

 the cup is more distinct, the tentacles are quite long and slender, and 

 are connected at the base by a Fig. 172. 



web (Fig. 172) ; this seems to 

 be a mere embryonic featm-e, as 

 I have noticed the same web in 

 several yoimg Campanularians. 

 The Hydrarium here figured at- 

 tained its present features at the 

 end of six months. The com- 

 munities are very small tufts, 

 barely perceptible to the naked 

 eye ; they appeared like a few 

 slender threads on the side of 

 the glass vessel in which the 

 Planula was raised ; I did not 

 succeed in raising the Hydrarium to observe its further develop- 

 ment. 



Massachusetts Bay (L. Agassiz). 



Cat. No. 276, Cape Cod, March, 1862, A. S. Bickmore. Medusa. 



Cat. No. 372, Nahant, September, 1863, A. Agassiz. Medusa. 



Museum Diagram No. 17, after A. Agassiz. 



Fig. 171. ip, young planula ; p', planula immediately before attaching itself. 

 Fig. 172. Single Hydra of the tuft of a Tima Hydrarium, greatly magnified. 



