ORIGIN OF HYDRA TUBA. 81 



This new animal was provided with a complement 

 of eight arms, yet so immature as to be of unequal 

 dimensions. Different groups under metamorphosis 

 showed the utmost irregularity in respect to evolu- 

 tion, both in their shape and proportions ; nor was it 

 until thirteen days later, or three weeks after their 

 birth, that any appeared with eight regular tentacula. 



Arrived at this point, the further development of 

 the nascent polyp is easily and satisfactorily traceable 

 the arms gradually become more numerous and at- 

 tenuated the body more elongated and conical the 

 stomachal cavity in the interior distinctly formed, and 

 the Hydra, now permanently fixed to some foreign 

 object, begins to fish for prey, and exercise all the 

 rapacity of its kind, until at length budding progeny 

 begin to sprout from its sides (PL I. fig. 4, g), and it 

 becomes the founder of a colony of kindred creatures, 

 after the manner described in the last chapter. 



Thus was a most perplexing problem solved the 

 Hydra tuba proved to have sprung from a Medusa. 



watch-glasses may be then inverted over the Planulse, and the 

 whole allowed to remain perfectly quiet for some days. 



Meantime the Planulae rising from the bottom, in the course 

 of metamorphosis, are intercepted from the surface of the water 

 by the watch-glass, to which they will adhere. This will some- 

 times happen in two days. After remaining there two or three 

 days longer, the watch-glasses should be removed to another 

 vessel of water and kept in an inclined position, the concavity 

 where the Planulre adhere being downwards. In the course of 

 about eight days many young Hydrse will be seen, pendent by 

 the prolonged apex. It is preferable to have only a few thus 

 adherent, as a number confuses the view. The subjects secured 

 in this manner are afterwards easily accessible. 



E 5 



