Opalina. 951 
Pl. XX). These are generally associated with other normal forms, 
but rarely may be the only sort present in the rectum. I have 
never seen these very large individuals in division. That they are 
not a distinct species but are really Opalinae caudatae is proven by 
numerous transitional stages between the two forms. The chromatin 
in their nuclei is often, through not always, aggregated into larger 
masses than is the case in normal nuclei of ordinary forms, and one 
suspects that the animals are not entirely normal, yet they are as 
active as other forms and are frequently found in large numbers 
in freshly taken material. 
It is chiefly the finding of these broad individuals of O. caudata 
that makes one a little doubtful as to the status of O. zelleri as a 
true species rather than as a condition of O. dimidiata. I have 
never seen similar enlarged forms of O. intestinalis or O. obtrigona. 
In one lot of O. ranarum from the rectum of an apparently normal 
Rana temporaria, there were, among a large number of ordinary forms, 
a few (about ten) individuals which were very much thicker than 
usual, being almost cylindrical. Their length was twice their width 
and their width half again as great as their thickness. I have not 
sectioned these thick individuals, but stained total preparations show 
nothing unusual in their appearance except the unusual thickness 
of the endosarc, the nuclei being a little less closely set in the endo- 
sare than in individuals of ordinary thickness. 
Licrer & Dusoscg (19046) describe certain individuals of 
O. saturnalis as very broad and thick in comparison with their 
length. In these individuals the increased thickness is due to the 
greatly increased thickness of the ectosarc, in which the alveoles 
and spherules are of remarkable size. In O. caudata and O. zellera 
and in the few thick individuals of O. ranarwm seen, the increased 
thickness of the body is due to the unusual development of the 
endosarc. Licrr & Dusoscg suspected that the broad individuals 
of O. saturnalis might be products of transverse division, but it is 
difficult to see what suggests this interpretation. 
It is well known (Zevier 1877, NeresHEemer 1907) that in the 
spring, when division becomes very rapid and most of the Opalinae 
become very small, some individuals in all species remain almost 
of full size, apparently not dividing any more rapidly than during 
the rest of the year. These large individuals do not encyst, but 
remain in the host and secure a continuance of its infection. It is 
possible that the great enlargement of some individuals is related 
in some way to the retardation of division. It is possible that 
