MEDUSA BIFIDA. 121 



curvatures. A row of 20 or 24 tentacula crowned the summit of the 

 cylinder, which row disappeared or was obliterated as the waving in its 

 vicinity deepened, and the diameter of the cylinder there expanded, that 

 is towards the summit. Concomitant on obliteration of the terminal row, 

 a new circle of tentacula, at first few, but gradually augmenting, was emerg- 

 ing from around the bulb, while the struggles of Meduste, into which the 

 waving strata were evolving, accomplished their liberation to swim uncon- 

 strained in the surrounding element. 



Before I speak of the period required for this evolution, together 

 with some incidental observations, I shall advert briefly to some facts of 

 early occurrence. 



I was then impressed with the belief of the original tentacula of the 

 hydra undergoing a change, being obliterated by a foreign substance im- 

 posed or generated on the disc, and that, as this substance, in fact com- 

 posing the roll, pillar, or cylinder, was dissipated, the tentacula resumed 

 their extension. Certain circumstances seemed to sanction my opinion. 



In the course of a long series of observations with which I was then 

 engaged, a single hydra having fallen from its place, it was transferred to 

 a separate vessel, wherein two years afterwards, its descendants were found 

 amounting to 45. Of these 42, along with itself, occupied the sides of the 

 vessel, and the remainder were afiixed to the bottom. With greater care, 

 perhaps, their numbers would have been augmented. 



In two years and eight months from commencement of the observa- 

 tions, one in the new vessel, which I conjectured the common progenitor 

 or parent hydra of this colony, dropped from its position on March 5. I 

 wish to specify dates as a guide to the period when naturalists may expect 

 a solution of their enquiries. 



Next day the figure of this subject seemed elongating, and in three 

 weeks the wonted pendulous roll appeared, as it lay in a watch-glass, as 

 in Plate XVIII. fig. 9 ; enlarged, fig. 10. 



Nothing but the colony of hydrse had occupied the vessel. 



The animal had fallen on March 5 ; it was delineated on March 25. 

 In five days the cylinder equalled about two-thirds of the length of the 

 whole subject, the remainder being smooth. It was about a third of the 



VOL. I. Q 



