208 M. M. Mercatr 
O. coracoidea, Buzzens. in Hana cyanophlyctis, °) 
O. obtrigona, STEIN » Hyla arborea, L.* *) (viridis Lavr.). 
*) Confirmed by my own observations. 
1) Ltaer & Dusoscg (1904)). 
®) Srerm (1867), ZELLER (1877), very rare in this host. 
3) Conte & Vaney (1902). 
4) T found in Naples one toad of this species whose rectum contained a few 
dozen Opalinae caudatae. 
5) BEZZENBERGER (1904). 
6) Zevter (1877), NeresHermer (1907), Mercaur (1907 a), 
*) Sroxrs (1884). 
5) Coun (1904). 
®) ZELLER (1877). 
All the species of Opalina which I have studied live chiefly at 
the upper end of the rectum of the host. A few individuals may 
be found scattered through the contents of the whole upper half of 
the rectum (this is especially true of O. obtrigona in Hyla arborea), 
but generally the parasites lie in one or more masses between the 
rectal contents on the one hand and rectal wall on the other. In 
frogs or toads which have been dead for some hours, the Opalinae 
are often found also in the lower part of the intestine, and occasion- 
ally, in frogs that were evidently diseased, I have found the 
posterior part of the intestine to contain some Opalinae. Several 
species of Opalina have been reported from the intestines, as well 
as the recta, of their hosts. It is possible that these reports are based 
on observations upon diseased frogs and toads, or upon those that 
were dead some time before they were examined. LkcEer & DuBosce 
(19046) report their new Opalina saturnalis as occurring in the whole 
intestine of Box boops. It would be of some interest to know if 
the whole intestine of normal, freshly killed fish of this species con- 
tains the parasites. 
Opalina caudata and O. intestinalis are rarely, if ever, found in 
the same individual host. In the two instances in which | have 
found O. zel’eri, O. dimidiata was also present. ZELLER also found 
these two forms together. NERESHEIMER (1907), the only other student 
who has recorded the occurrence of O. zelleri, does not say whether 
he found it with O. dimidiata or not. There is a little doubt of the 
independence of the two species. 
The frequency of infection of the several hosts by the several 
species is shown for the animals I examined in the following table. *) 
1) Records were not kept of a number of the hosts which were killed early 
in the fall of 1906, or. of most killed in Naples. 
