'Opalina mitotica. 8 
the spring when they are more easily captured — is probably due 
to the porasites leaving the recta of the adult salamanders in the 
spring when they go to the water to breed. 
In its general form Opalina mitotica resembles O. öntestinalis 
(Figs. 1—6, 8 and 10), being a spindle pointed posteriorly and rounded 
anteriorly and with its anterior end bent to one side, as in the case 
with all known Opalinae. "The anterior rounded end is wedge-shaped, 
to that in edge view it looks almost sharp instead of broadly rounded 
(Figs. 3 and 4). In this regard this species resembles Opalina zelleri 
and the little known 0. flava. The relative general proportions are 
about as in Opalina intestinalis. "The size of the specimens examined 
varied from a length of 94 mm and a greatest breadth of 23 mm 
in the largest individuals to a length of 52 mm and a with of 
9 mm in the smallest.!) Of course in the spring much smaller indi- 
viduals would be found. 
There is generally a somewhat greater distance between the 
nuclei than in Opalina intestinalis. The two nuclei when fully formed 
are never connected by a strand as is so often the case in 0. intesti- 
nalıs and O. caudata. 
In size and number of the plastids 0. mitotica agress with O. 
intestinalis. The endosarc plastids are disc-shaped, the flat sides 
of the disc being parallel with the surface of body (Figs. 14 
and 15). Upon focussing near the edge of the animal the dises, 
in edge view, appear linear. In the character of the ectosarc and 
endosarc O. mitotica and O. intestinalis closely agree. In individuals 
stained with carmine and picric acid the endosare is red and the 
ectosarc green. The ectosarc plastids are large and irregular and 
stain differently from the endosarc plastids. 
None of the preparations I have show an excretory vacuole, 
but in a few individuals there is an axial region which looks exactly 
as does the axial region of an Opalina intestinalis with a well deve- 
loped axial vacuole, which has been killed in corosive sublimate- 
acetic acid and stained in DELAFIELD’s haematoxylin (cf. METcALF 1907). 
It seems therefore that ©. mitotica has a well developed axial vacuole, 
but study of living individuals is needed to confirm this point with 
certainty. If a well developed excretory vacuole is present in this 
species, cursory exmmination of living individuals which have been 
kept a few hours in normal salt solution would doubtless show a 
1) Excepting two individuals just from division, 
Zool. Jahrb., Suppl. XV (Festschrift für J. W. Spengel Bd. I). 6 
