Opalina. 319 
that of O. dimidiata, but it is difficult to see how he knew that the 
reproductive stages studied belonged to 0. gellert and not to 
O. dimidiata which was living in the same host. I have once seen 
an individual of O. zelleri in longitudinal divison, the phenomena 
being as in O. dimidiata. 
I have no constant opinion as to the distinctness of O. zelleri 
from O. dimidiata. 
Chronological Review of the Literature of Opalina.') 
Opalina was first mentioned 
by LeEEuwENHOEK in 1685. In his 
Opera omnia (1722) he quotes the 
earlier record of finding innumer- 
able animalculae of various sizes 
and forms in the foeces of the 
frog. One of these figured seems A B 
in all probability to have been Rano 
O. ranarum (Text Fig. XII, B). A= LEEUWENHOEK’S fens: of animalculae 
other may have been O. dimidiata trom the rectum of frogs: A may be 
(Text Fig. XII, A) [not O.intestinakts 0. dimidiata; B is almost surely 
as Kent (1881—1882) supposed ].*) O. ranarum. 
One hundred years later than Leruwennoek, Biocna (1782, p. 36, 
Taf. XXIII) described and figured two forms from the alimentary 
canal of the frog, which he called Hirudo intestinalis and Chaos in- 
testinalis cordiformis. The former was probably O. dimidiata or 
) Only papers and books which include observations upon Opalina, or dis- 
cussions based definitely upon conditions in Opalina, are included in this review. 
General discussions which do not especially mention Opalina are omitted, so also 
are most text books which refer but briefly to observations upon Opalina made 
by others than the authors of the books in question. I have endeavored, with 
these exceptions, to make the review as complete as possible, but doubtless I have 
failed to find numerous references to the genus. I should cordially appreciate the 
kindness of any one who would direct my attention to references to Opalina not 
mentioned in this review. 
*) Throughout this review of the literature my own comments are included 
within brackets. 
