630 ' C. H. MARTIN. 
ences are often very great, there is frequently the additional 
factor of the change of host (e.g. Hemosporidia). In the 
case of the animal Ophryodendron of which some descrip- 
tion is given in the following pages, such an explanation of 
the dimorphism in terms of the Amphigonous and Schizo- 
gonous stages of a life cycle is absolutely excluded. For 
although conjugation has never been described in this form 
(Koch’s theory will be dealt with later), yet from the presence 
of a micronucleus there is very reason to predict, that as in 
other Acinetaria, conjugation will be found to occur of a kind 
absolutely similar to the process of conjugation in the Cili- 
ates. 
And it is again interesting to observe that Ophryoden- 
dron is the only free living heterokaryote (i.e. Ciliate or 
Acinetarian)—in which dimorphism! has been observed. 
Ophryodendron is a somewhat aberrant Acinetarian 
frequently found as an ectoparasite on Hydroids, and also, 
though more rarely, on Crustacea. As has long been known, 
it occurs under two remarkably different forms; (a) the pro- 
boscidiform individual, and (b) the vermiform or Lageniform 
individual. 
The proboscidiform individual is characterised (1) by the 
more or less pyriform shape of the body (in Ophryoden- 
dron sertulariz the body is compressed), 
(2) By the absence of a stalk (this may be present in some 
forms, e.g. Ophryodendron trinacria), and 
(3) By the presence of a long, very contractile proboscis 
furnished with rows of tentacles. 
The vermiform individual is characterised— 
(1) By its elongate cylindrical body, 
(2) By the presence of a long solid stalk which passes into 
the posterior end of the body, and 
(5) By the absence of a proboscis. 
It is obvious that the difference between the two dimorphic 
forms in the case of Ophryodendron is very great (so 
1 By the term dimorphism the occurrence of two different repro- 
ductive forms in the same species is here meant. 
