214 BUNTING. [Vor UX. 
terminal cells of these two layers then unite, and we have an 
appearance as though the umbrella had been formed by the 
infolding of the external ectoderm. At about this same time 
the velum forms, and the medusa with all its organs complete, 
and containing the adult sexual products, is now ready to 
escape from the blastostyle, and lead an independent existence. 
THEORETICAL. 
The discovery that, at Wood’s Holl, colonies of Podocoryne 
and of Hydractinia are found side by side under similar condi- 
tions of life, and yet appearing in such different proportions, 
is of much interest. Surely, there is opportunity to learn here 
a lesson in the phylogenetic history of the Hydromedusae. 
What are we to conclude? Is Hydractinia very slowly devel- 
oping into the more complicated form of Podocoryne with 
its free swimming medusa, or is Podocoryne gradually form- 
ing the hydroid with the retrograde blastostyle and gono- 
phore? We must consider which is best adapted to survive in 
the struggle for existence. The sex-cells carried in these very 
small medusa subjected to the influence of the waves, would 
be much more likely to fall into places unfavorable for 
development than would the sex-cells carried in the gonophore. 
Moreover, we have evident signs of degeneration in both 
blastostyle and gonophore of Hydractinia, to quote Dr. W. K. 
Brooks : ‘In Hydractinia, the cormi of which are so similar 
to those of Podocoryne that a drawing of one will correctly 
represent the other, the life history begins to simplify itself 
by the degradation of the sexual medusa into sessile buds, or 
reproductive organs which, however, still retain traces of their 
former independent locomotor existence.” 
Sidney Hickson takes a different view of the subject ; while 
not speaking directly of Hydractinia and Podocoryne, he traces 
the gradual development of the medusa through the gonophores 
of forms similar to Hydractinia, from the simplified gonophores 
of Allopora and Distichopora. 
Until more evidence is collected to support this view, it 
seems more logical to adhere to that which considers Hydractinia 
