154 REPRODUCTION. 



from the hydriform trophosome of the Hydroida, are destined to undergo further development 

 and enjoy an independent existence like that of the hydroid planoblasts. But notwithstanding 

 this difference the analogy is still close and interesting ; for the more simultaneous occurrence of 

 the transverse constrictions which result in the formation of a pile of discs before their ultimate 

 detachment in the scyphodoma has but little significance ; while, as we have already seen, the 

 hydranths successively produced and detached from the stem \\\ Tubularia, are formed not by a 

 process of budding, but by one of metamorphosis which shows itself in growth with change of 

 form in the distal extremity of the stem in this hydroid, — a mode very similar to that by which 

 the successive terminal discs or rpJiyra are developed from the scypliosioma. 



