SOME OBSERVATIONS ON ACINETARIA. 659 
represented end on, and it is only safe to say that it certainly 
does not furnish the required evidence of the transformation 
of the vermiform into the proboscidiform individual. 
It will thus be seen that there are two main sources of 
error in attempting the proof of this theory from a mere 
examination of fixed specimens—(1) The presence of young 
vermiform individuals which have broken loose from the 
proboscidiform individual, but have not yet developed their 
stalk; (2) the presence of degenerating proboscidian forms 
seen in a horizontal plane. 
Finally the presence of active ciliated embryos in the 
vermiform individuals show that they can hardly be regarded 
as immature forms, and it will be evident, from what has 
been said above as to the structure of the two individuals, 
that the change from the vermiform individual to the pro- 
boscidiform individual would need to be of a far more radical 
nature than Fraipont and Sand have imagined. 
(4) Hincks’ Theory of Dimorphism.—Of the various 
theories put forward to explain the appearance of the two 
individuals in Ophryodendron, I think that the obser- 
vations given above show clearly that Hincks’ theory of 
dimorphism is alone in accordance with the facts. ‘he 
proboscidiform individual gives rise by a process of external 
budding to the vermiform individual; both the proboscidi- 
form and the vermiform individual can give rise to ciliated 
buds, which are already ciliated before the process of division 
is complete. This last fact gives the explanation of the two 
sizes of ciliated embryo found by Claparéde and Lachmann, 
I have never been able to follow the history of the ciliated 
buds from the vermiform individual, but from the fact that 
the smallest free vermiform individual that I have been able 
to find, after looking over many hundreds, was far larger 
than the largest free ciliate embryo found, I believe the 
ciliate embryos of both forms always develop into probos- 
cidiform individuals. 
From an evolutionary standpoint, it would seem that the 
dimorphism of Ophryodendron presents a case which is 
VOL, 53, PART 3,—NEW SERIRS. 45 
