SOME OBSERVATIONS ON ACINETARIA. 661 
produced, was in such perfect accordance with the environ- 
ment, that no further change would be necessary. 
It is very difficult to regard this explanation as being in 
any way adequate when it is remembered how different the 
environment of a vermiform individual of Ophryodendron 
trinacria, which is attached to a free swimming copepod, 
must be from that of the vermiform individual of Ophryo- 
dendron abietinum, which is to a large extent a tiue 
external parasite of a hydroid. On the other hand, if the 
number of embryos of the same type produced by these two 
forms is to be regarded as some measure of their success in 
the struggle for existence, there is distinct evidence that the 
vermiform type cannot be regarded as so successful a form 
as the proboscidiform type. 
Diagram of the life cycle. 
The stages actually followed in living specimens are indi- 
cated by black arrows. ‘The probable development of the 
ciliate buds of the vermiform individual is shown by a dotted 
line. 
(by external budding 
Proboscidiform individuals >Vermiform individual. 
/ | 
/ ! 
Ciliated buds. Ciliated buds. 
‘X\ 4 
Proboscidiform individual, 
10. Summary or Resorts. 
(1) Ophryodendron abietinum is a true ectoparasite 
of the hydroid to which it is attached, and _ its 
contained nematocysts are derived from its host. 
