OPALINA AND NYCTOTHERUS Zao 
that in Leeuwenhoek’s description “ Opalinae and Nyctotherus 
can be recognized with sufficient certainty.”* No species are 
indicated, though the two which I have mentioned must, I 
think, have been intended. Saville Kent, however, had 
previously identified Leeuwenhoek’s Fig. A as Opalina 
intestinalis :” but this is highly improbable, because there is 
no certain record of this species having ever been found in 
either R. temporaria or R. esculenta.’ 
Metcalf, who has studied the Opalinidae in greater detail 
than any other specialist, writes of Leeuwenhoek’s observations 
as follows : * 
‘“ Opalina was first mentioned [?] by Leeuwenhoek in 
1685° [?]. In his Opera omnia (1722) he quotes the earlier 
record [?] of finding innumerable animalculae [sic] of 
various sizes and forms in the foeces [sic] of the frog. One 
of these figured [L.’s Fig. B] seems in all probability to have 
been O. ranarum. Another may have been O. dimidiata 
DRG ya cates. diag 
From this it seems to me that Metcalf cannot have studied 
Leeuwenhoek’s works or words very carefully, nor does he 
- appear to appreciate the difficulties of his own interpretation. 
If—as he suggests, and as I am convinced—Fig. A represents 
O. dimidiata, then the smaller rounded form (Fig. B) can 
hardly have been O. ranarum. For this species is at least as 
large as O. dimidiata, and occurs typically in a different host— 
RR. temporaria.” Consequently, if Metcalf’s interpretation 
were correct, it would leave the small size of Fig. B un- 
' Biitschli (1887-89), Vol. III, p. 1101. The date of the observations is 
wrongly given, however, as 1687. Cf. also zbzd., pp. 1718 and 1721. 
* Kent (1881-82), Vol. II, p. 562. 
* Opalina (Protoopalina) intestinalis is a species proper to Bombinator— 
not Rana. Cf. Metcalf (1923), p. 51. Kent’s error was first noted by 
Metcalf (1909), p. 319. 
* Metcalf (1909), p. 319. My comments are interpolated in square 
brackets for the sake of brevity. In my opinion this single sentence 
contains at least six mistakes, but it seems unnecessary to do more than 
indicate them. 
° In a later work (Metcalf, 1923, p. 438) the date is given as 1865 [! ]— 
presumably by misprint of the first date (1685), which was itself incorrect. 
Little errors of this sort abound in nearly all discussions of L.’s work. 
° I know of no certain record of O. ranarwm having been found in R. 
esculenta, or of O. dimidiata from R. temporaria. Cf. also Metcalf (1923). 
