ON BALANTIDIUM COLI (MALMSTEN) AND
BALANTIDIUM SUIS (SP. NOV.), WITH
AN ACCOUNT OF THEIR NEURO-
A THESIS ACCEPTED IN PARTIAL SATISFACTION OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
AT THE UNIVERSITY OF CALIFORNIA
JAMES DALEY McDONALD
' ' *-
UNIVERSITY OF CALIFORNIA PUBLICATIONS
Vol. 20, No. 10, pp. 243-300, pis. 27-28, 15 figures in text May 8, 1922
ON BALANTIDIUM COLI (MALMSTEN) AND
BALANTIDIUM SUIS (SP. NOV.), WITH
AN ACCOUNT OF THEIR NEURO-
j. DALEY MCDONALD
UNIVERSITY OF CALIFORNIA PRESS
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6. On the Orientation of Erytliropsis, by Charles Atwood Kofoid and Olive
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* ' J J
ON BALANTIDIUM COL I (Malmsten) AND BALANTIDIUM St
WITH AN ACCOUNT OF THE i NEUROMOTOR APPARj
Submitted in partial fulfillment of the requir*
for the degree of Doctor of Philosophy
Is Approved : ci-fr^ Pasadena, California
UNIVERSITY OF CALIFORNIA PUBLICATIONS
Vol. 20, No. 10, pp. 243-300, pis. 27-28, 15 figures in text May 8, 1922
ON BALANTIDIUM COLI (MALMSTEN) AND
BALANTIDIUM SUIS (SP. NOV.), WITH
AN ACCOUNT OF THEIR NEURO-
j. DALEY MCDONALD
Acknowledgments : 245
Material and technique 245
Occurrence and geographic distribution 246
Studies of living organisms 246
Systematic position of genus and species 248
Balantidium coli 249
Balantidium suis sp. nov 250
Method and use of measurements 254
Other specific characters 258
Balantidium from man 261
Ectoplasmic structures 263
Pellicle , 263
Basal apparatus of cilia 271
Ciliary movements 273
Oral plug 280
Contractile vacuoles 280
Endoplasmic structures 282
Food vacuoles , '. 282
Neuromotor apparatus 284
Motorium .' 285
Circumoesophageal fiber 285
Adoral ciliary fiber 286
244 University of California Publications in Zoology [VOL. 20
Adoral ciliary rootlets 286
Radial fibers . 286
Literature cited , 294
Explanation of plates 298
The earliest observation of Protozoa of the genus Balantidium has
in several instances been accredited to Antony von Leeuwenhoek
(1708). During an attack of dysentery he detected motile organisms
in the discharges. At that time no discrimination had been made
between ciliated and flagellated protozoa and his account of his obser-
vations is not sufficiently complete to make possible the classification
of the organisms which he found. However, he stated that they were
about the size of red blood corpuscles, which would indicate that they
were intestinal flagellates and not Balantidium, which is very much
Malmsten (1857) was the first to describe Balantidium coli. This
species has become better known than the other species of the genus,
due to its being the cause of a specific dysentery known as balantidiasis.
Two persons suffering from this disease came to Malmsten for medical
attention during 1856-57. Pie was assisted in the study of protozoans
which he found in the excreta from these two patients by the zoologist
Loven who believed that the parasites were new to science and so pre-
pared a careful description of them accompanied by figures. For the
organism they suggested the name Paramoecium ( ?) coli. Since that
time infections with Balantiddum coli have been reported in increasing
numbers and some cytological studies 'have been made, though much
more attention has been given to the problems of prophylaxis and
treatment of the disease which this species causes than to the parasite
The first record of Balantidium coli as a parasite of pigs was made
by Leuckart (1861). Stein (1862) also studied these forms from pigs
and he was the first to assign them to the genus Balantidium. The
genus had been established by Claparede and Lachmann (1858) with
Balantidium entozoon from the frog as the type species. More recently
Strong (1904), Brumpt (1909), Walker (1913), and others have car-
ried on investigations on this parasite of pigs in order to become
acquainted with the problems involved in the infection of man.
1922] McDonald: On Balantidium eoli and Balantidium suis 245
It has been my privilege to study the morphology of Batantidium
coli and Balantidium suis (sp. nov.) under the direction of Professor
Charles A. Kof oid, to whom I am indebted for helpful suggestions and
for oversight of the entire work. Acknowledgment is due Professor
William W. Cort for many valuable criticisms. I also take this oppor-
tunity to express my appreciation of the courtesy of Mr. E. B. Brown,
superintendent of the Oakland Meat and Packing Company, who
kindly granted me permission to work in the company's abattoir and
also facilitated the work in every possible way.
MATERIAL AND TECHNIQUE
The material for these studies was obtained almost exclusively from
pigs killed by the Oakland Meat and Packing Company, Stockyards,
California. At their abattoir I was permitted to work in the room
where the pigs were dressed, which made it possible to obtain the
material from the intestine before it had cooled below the normal body
temperature. To determine the presence of the balantidia a small slit
was made in the caecum and a drop of the contents withdrawn with
a pipette. This drop was quickly placed on a warm slide and exam-
ined with a microscope. If the animals were present they would be
detected very readily for they are exceedingly active ; in most cases
they occurred in numbers sufficiently large that from one to ten could
be seen in every field when a 16 mm. objective was used. This method
was rapid enough to allow all pigs to be examined as fast as they were
killed and dressed.
A sample from the caecum was not relied upon as critical in the
determination of infection until examination of the entire length of
the intestine had been made in several instances. In order to discover
the normal distribution throughout the intestine it was removed entire
and taken to the laboratory of the abattoir. Incisions were made every
one or two feet, beginning with the duodenum and continuing to the
rectum, and samples examined from each of these incisions. In no
cases were balantidia found more than three feet above the ileocaecal
valve, and only in two or three instances were any at all present in
246 University of California Publications in Zoology [ VoL - 20
the small intestine. In the caecum and first three or four feet of the
colon the balantidia were always more active and more numerous than
elsewhere. Posteriorly from this region they were found in progressive
stages of encystment until in the rectum the majority were completely
OCCURRENCE AND GEOGRAPHIC DISTRIBUTION
Approximately 200 pigs were examined. They had been raised in
the Sacramento Valley, except for one lot from Los Banos, California,
and a lot from the state of Nevada. Of the 200 pigs examined 68
per cent were infected. The examinations were made at nine separate
times between September, 1913, and May, 1918, ten to sixty individuals
being examined each time. In five of the nine lots every pig was
found to be infected. The lowest percentage of infection was 13 per
cent, in the lot shipped from Nevada. This indicates a very general
infection of pigs with Balantidium in this region of the United States.
Stiles (cit. Strong, 1904), Bel and Couret (1910), and others have
previously found the organisms in pigs in the United States. Leuckart
(1861), working in Germany, was the first to find Balantidium in pigs.
Since then Stein (1862), Eckecrantz (1869), and Prowazek (1913)
have reported them from the same country. In 1871 Wising noted
their occurrence in pigs in Sweden. Grassi (1882) and Calandruccio
(1888) have found the parasites in swine in Italy. Rapchevski (1882)
reported the occurrence of balantidia in Russia. In France they have
been found in pigs by Railliet (1886), Neumann (1888), and Brumpt
(1909). Strong (1904), Walker (1913), and several others have
noted the occurrence in pigs in the Philippine Islands. Similar reports
from China have been made by Maxwell (1912), and Mason (1919) ;
from Cuba by Taboadela (1911) ; and from South America by Bayana
(1918). These citations indicate that BalantiMum coli is probably as
widely distributed geographically as is its host, the pig.
STUDIES OF LIVING ORGANISMS
The balantidia are very sensitive to changes of temperature. When
the medium in which they are swimming is cooled a few degrees they
slow up their movements very decidedly. After a time they become
almost perfectly spherical, in which form their activitiy is restricted
to a rotary motion with little or no progression. In this condition they
will live for six or eight hours at ordinary room temperature.
1922] McDonald: On Balantidium coli and Balantidium suis 247
In order to avoid the deleterious effects caused by cooling and by
increased bacterial action, most of the studies on living organisms were
made at the abattoir. When continuous observation over a long period
was desired, however, the material was conveyed to the laboratory in
thermos bottles and kept in the incubator at 37.5 C. In tfris~manner
material could be kept for three days. Ultimate degeneration of the
organisms seemed to be due more to the increase in the bacterial con-
tent of the medium than to any other cause. During observation either
an electric warm stage or the microscope warm oven designed by Long
(1912) was employed. Of the several vital stains used, neutral
red proved most satisfactory in the differentiation of the neuromotor
Fixation and staining. The following fixatives were used : Schau-
dinn's fluid, Zenker's fluid, formalin, osmic acid, and picromercuric
fluid (according to the formula by A. D. Drew, used by Yocom, 1912).
Quick action was one of the most important factors in the fixation,
and was usually obtained by having the killing fluid hot (60-80 C.)
and using an amount at least equal to the amount of the material to
be fixed. Frequently the action was so nearly instantaneous that the
cilia on the killed animals retained their exact relative position (see
fig. N). After fixation the material was thoroughly washed, iodine
alcohol being used if mercurial salts were present. Material was pre-
served in 70 per cent alcohol.
Before staining, the preserved material was usually concen-
trated by elimination of lighter debris by centrifuging and the heavier
by sedimentation. Water was found to be a more satisfactory medium
for these operations than either alcohol or salt solutions. In case sec-
tions were to be made, additional care was taken in the concentration
process and then the material was handled according to the methods
employed by Metcalf (1909) and by Sharp (1914).
Iron haematoxylin gave uniformly the best results in staining. For
cysts, however, on account of their imperviousness, it was necessary to
use Delafield's haematoxylin to which had been added a small amount
of acetic acid. In addition to the first mentioned stain, Mallory's con-
nective tissue stain was used on sections.
University of California Publications in Zoology [ V L - 20
SYSTEMATIC POSITION OF GENUS AND SPECIES
Claparede and Lachmann (1858) removed Bursaria entozoon from
the genus in which it had been placed by Ehrenberg (1838) and
created for it the new genus Balantidium. This genus was of the
family Bursaridae and the order Heterotricha. The twenty-two species
of the genus that have been described to date are listed below.
KNOWN SPEOIES OF THE GENUS BALANTIDIUM
Original description by
Entz, Sr., 1888
Entz, Jr., 1913
Entz, Jr., 1913
Neiva et al, 1914
Ban a esculenta
Eucope, Broda sp.?
1922] McDonald: On Balantidium coli and Balantidium suis 249
The wide diversity of hosts, ranging from hydroids and crustaceans
to the warm-blooded vertebrates, including man, must demand a wide
versatility on the part of the parasite. Considerable structural varia-
tion is apparent even on cursory examination, and some of these
structural differences might be sufficiently marked to servTT for generic
differentiation. A new generic division would seem desirable, but the
suggestions of Biitschli (1884) and Schweier (1900) in this direction
have not been generally accepted.
BALANTIDIUM COLI MALMSTEN (1857)
Paramoecium (?} coli Malmsten, 1857.
Plagiotoma coli, Claparede and Lachmann, 1858.
Leucophyra coli, Stein, 1860.
Holophyra coli, Leuckart, 1861.
Balantidium coli, Stein, 1862.
Up to the present time only one species, Balantidium coli, has been
described as parasitic in pigs. It was first described by Malmsten
(1857) who, noting its likeness to Paramoecium colpoda (Ehrenberg),
suggested the name Paramoecium (?) coli. During the following year,
Claparede and Lachmann (1858) reproduced one of Malmsten 's orig-
inal figures and after considering his description transferred the
species to the genus Plagiotoma. In 1860, Stein, using the description
by Malmsten (1857), pointed out that the organism was not a Para-
moecium and Relieved that it properly belonged in the genus Leuco-
phyra. Leuckart in 1861 discovered a ciliate in the intestine of pigs
which he concluded was identical with the one already described, but
he was not satisfied with the genus to which it had been assigned by
Stein (1861) and believed that its closest relation was with Holophyra
in which genus it should be placed. In. 1863 he still retained this view
but suggested the appropriateness of the establishment of a new genus.
But Stein (1862) had already recognized those characters of the
species which showed its close relation to Balantidium entozoon and
had placed it in the genus Balantidium.
During the present investigation the following specific character-
istics have been found very constant. The individuals of the species
Balantidium coli are ovoid in form, the more pointed end being an-
terior; length varies from 30/* to 150/t; breadth varies from 25,/A to
120ju, ; in the majority of individuals the length is 1.3 times the breadth ;
the greatest transverse diameter intersects the longitudinal axis poster-
250 University of California Publications in Zoology [ VoL - 20
ior to its midpoint; the adoral zone is approximately terminal, and
the anterior tip of the body lies within it; the plane of demarcation
between the apical cone of the ectoplasm and the endoplasm is approx-
imately at right angles to the long axis of the body ; the macronucleus
is elongate but the length usually does not exceed three times the
breadth; two contractile vacuoles are present, a smaller one located
anteriorly and a larger one located posteriorly; a posterior cytopyge
is usually distinctly visible.
BALANTIDIUM suis SP. NOV.
Early in the work of examining pigs for Balantidium coli it became
evident that this protozoan showed extreme variation in shape. In
many instances the diversity occurred among individuals from the
same host. Further observations led me to believe that there were
two fairly distinct types, the one, longer and more slender as compared
with the other which was distinctly ovoid. Measurements have been
recorded by various writers of Balantidium coli from man. Malmsten
(1857) in the original description gave the length as 60-10CV; breadth,
50-70/i. Solojew (1901) recorded the length as 65/*, the breadth as
40/A. Wising (1871) states that the length varies from 50-100/z, while
the breadth varies from 40-50/*. Prowazek (1913) gave the length as
52-71/x, the breadth, 40-58/*. Leuckart (1861) measured balantidia
from swine and found the length to be 75-110/x and the breadth 70/x.
Still others give dimensions, but all are inadequate for the determina-
tion of the occurrence of types with distinct proportions. First, with
one or two exceptions all dimensions have been taken of balantidia
found in man, and from these it might not be safe to draw conclusions
regarding diversity among those found in pigs. In the second place,
the measurements given are either averages or else represent extreme
limits. In either case they are practically useless in determining indi-
vidual variations, for even in the case of extreme types the range
between limits is so great that two, or even more, distinct types, based
on proportions of breadth to length, might be included. Nowhere
has there been found a series of individual measurements which would
make it possible to determine whether variations were continuous or
discontinuous. To obtain such a series of measurements was the pur-
pose of the phase of the work about to be described.
Material which was to be used in taking the measurements was
killed and preserved with all possible care. Hot Schaudinn's fluid
was used in all cases, the material being quickly and thoroughly mixed
1922] McDonald: On Balantid/ium coli and Balantidium suis 251
into a large quantity of it so that action would be as nearly instan-
taneous as possible, thus avoiding distortion. Osmic acid vapor was
tried but Schaudinn's fluid gave equally good results and was more
convenient for manipulation. Material was never allowed to cool
before fixing, for on cooling the individuals tend to become spherical.
Several attempts were made to measure living organisms but their
ceaseless activity at normal temperature (.37.5 C) made this almost
impossible and slowing them up by the use of Irish moss or by cooling,
as mentioned above, caused them to become distorted. If there were
changes due to fixation, the logical expectation would be that the error
would be on the side of conservatism for such changes would tend to
obliterate rather than accentuate the division into two groups ; for the
shape of the elongate forms would be more changed by the fixative,
the tendency being for them to shorten and broaden and thus approach
the ovoid type. However, in the method of fixation used, I am sure
that distortion was so slight as to be negligible.
Following fixation the material was carefully washed and carried
slowly through the lower grades of alcohol to 70 per cent in which
the material was kept for measuring. A drop of the material from
which measurements were to be taken was placed on a slide, covered
with a coverglass, the excess of fluid removed, and the edges sealed
with vaseline to prevent evaporation. Just enough fluid was removed
from under the coverglass to reduce the depth of the medium so that
the majority of the animals would lie flat, and yet not enough to allow
the coverglass to exert any pressure. The exertion of pressure on the
animals, however, would ordinarily be prevented by the presence of
large particles of foreign material. The object of having animals lie
flat on the slide was to avoid the error which would otherwise be caused
by foreshortening. A slight elevation of one end would make con-
siderable error in the determination of the length of the animal.
The slide was then placed on the microscope and systematically
examined by the use of the mechanical stage. Beginning at the upper
left-hand corner and progressing as one would in reading a book, every
individual encountered in the survey was measured. The only excep-
tions made were in case the animal was not lying flat or showed marked
signs of distortion. This procedure avoided selection which might
unconsciously be made by the observer. For making the measurements
a 4 mm. objective was used in combination with an ocular-micrometer
inserted in 9x compensating ocular. With the magnification given by
this combination the limit of error did not exceed one micron.
University of California Publications in Zoology [VOL. 20
The longitudinal axis and the longest transverse axis of each indi-
vidual were measured, and the ratio of length to breadth computed
(see Table I).
COMPARATIVE MEASUREMENTS OF
INDIVIDUALS FROM PIG No. 1
(Bal. suis, with five exceptions)
ONE HUNDRED INDIVIDUALS EACH OF
AND BALANTIDIUM suis
INDIVIDUALS FROM PIG No. 4
(Bal. coli, with one exception)
* Other characters showed that these individuals were of the other species rep-
resented in the table.
1922] McDonald: On Bala/ntid/ium coU and Ealantidium suis 253
TABLE I (Continued}
INDIVIDUALS FROM PIG No. 1
(Bal. suis, with five exceptions)
INDIVIDUALS FROM PIG No. 4
(Bal. coli, with one exception)
* Other characters showed that these individuals were of the other species rep-
resented in the table.
University of California Publications in Zoology [ V L. 20
TABLE I (Continued}
INDIVIDUALS FROM Pia No. 1
(Bal. suis, with five exceptions)
INDIVIDUALS FROM PIG No. 4
(Bal. coli, with one exception)
Length in Breadth in
While taking the measurements of each individual, observations were
made regarding the position of the mouth, the type and size of macro-
nucleus, number and location of contractile vacuoles, and any other
characters which might aid in differentiation.
In the handling of the data on dimensions I have followed in a
general way the method used by Jennings (1908) in differentiating
races of Paratniaecium. For the purpose of this work, however, the
results seemed more lucid if, instead of plotting length and breadth
along separate axes, the ratio of length to breadth was computed for
each individual and if these ratios were then plotted on the abscissa
while the numbers of individuals having each of these ratios were
plotted on the ordinate. In computing the ratios the quotient was
carried to the second decimal place. But in the construction of the
curves only intervals of tenths (or first decimal place) were used;
thus, for example, all ratios occurring between 1.25 and 1.34 inclusive
were grouped as if they were 1.3. This had two advantages : first, it
produced a smoother, steeper curve than would result if smaller inter-
vals were taken, using the same number of individuals measured, and
emphasized group rather than individual variations. Second, this
grouping reduced any error which might result from the observer
showing a preference for one graduation of the micrometer when
1922] McDonald: On Balantidium coli and Balantidium suis 255
an individual measured more than one but less than another whole
division of the scale ; e.g., such a preference might result in the tabu-
lation of several individuals having a length of 72/t, and of none with
a length of 7 1/*,, though in reality all lay within these two limits and
as many were as near to one as to the other.
As previously mentioned, the graduations along the ordinate
represent the number of individuals, each small interval representing
one individual. In Jennings' (1908) work these intervals represent
percentages of the total number of individuals. But it happens that
I.I 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6
Fig. A. Graphic representation of the variation in the ratio of length to
breadth among 200 Balantidium chosen at random from samples of material taken
from several different pigs. The number of individuals is measured on the ordi-
nate, the ratios on the abscissa. The dotted line is the curve resulting from the
combination of the two curves shown in figure B, superimposed here to facilitate
in the graphs shown in figures B and C, the number of individuals
showing a certain ratio is identical with the percentage of the total,
for in these cases the total is 100 individuals.
Figure A represents graphically the result of the first attempt
to determine the existence of different types. Measurements were
made of 200 individuals. At least ten slides were used in getting
these measurements and they were prepared from samples taken from
nearly as many different pigs. It will be noted that the curve pro-
duced by plotting the ratios of these individuals is decidedly bimodal.
One mode represents those individuals which are approximately 1.2
times as long as wide, while the other represents those which are 1.6
to 1.8 times as long as wide.
These findings seemed to fully justify my early suspicions that
there were two very different types of balantidia parasitic in pigs.
University of California Publications in Zoology [VOL. 20
But it was decided to conduct one more experiment, for corroboration,
under slightly different conditions and with especial care in fixation
of the material. It had been noted that though often both types
occurred in the same pig (which was the case in most of the samples
used in the first measurements), still one type might be greatly in
excess, or there might be only one type present. In getting material
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1
2.2 2.3 2.4 2.5 2.6
Fig. B. Graphic representation of the difference in ratio of length to breadth
between two carefully selected lots, of 100 individuals each, of Balantidium from
separate hosts. The continuous line represents those from one pig (nearly all are
Balantidium coli) ; the broken line, those from the other pig (nearly pure infection
with Balantidium suis).
Fig. C. This graph shows the variation in the ratio of length to breadth among
100 Balantidium secured from a case of balantidiasis in man.
for this second set of measurements, it seemed best to take it from pigs
which had, as nearly as could be determined, pure infections of the
respective types. Fortunately these requirements were fulfilled in
the next lot of pigs examined. Both samples of material, the one con-
taining the ovoid and the one containing the elongate type, were
treated in exactly the same way. They were killed at the same time
1922] McDonald: On Balantidium eoli and Balantidium suis 257
with the same fluid (in separate containers) and in the same water
bath. Thence to 70 per cent alcohol the treatment continued identical.
One hundred individuals from each sample of material were measured.
From these measurements the graphs shown in figure B were con-
structed in the same manner as the preyious one, except" that the
curves of the separate samples were plotted separately on the same
axis. The continuous line represents the individuals from one pig and
the broken line those from the other. The mode of the first curve
occurs at 1.3. If the ratios 1.2 and 1.4 be included with 1.3, it is found
that 80 per cent came within these limits. Of the entire number of
individuals in the lot only one showed a ratio of 1.6 and one as high
as 1.7, while there were none with a higher ratio. The second curve
reaches its highest point at 2.0, while 71 per cent of the entire number
measured is included between 1.8 and 2.2. A number of individuals
have ratios above 2.2, while one had a ratio as great as 2.7. Five indi-
viduals have ratios below 1.6, at which point the curves begin to over-
lap ; but in practically every one of these individuals there were
observed characters (which are discussed below) that made it quite
evident that they were really of the type represented by the other
Upon comparing figures A and B their likeness is very striking,
the second being corroborative of the results shown by the first. That
both are bimodal is evident. However, the low points, the point of
demarcation of the two groups, do not occur at the same place ;
in the first it is at 1.4, while in the second it occurs at 1.6. Also the
median of the first mode in figure A occurs at 1.2 while in figure B
it is at 1.3, and the median of the second mode in figure A is at 1.7
while in figure B it occurs at 2.0 ; that is, in figure A the entire curve
is shifted to the left, meaning that all ratios are decreased or that all
individuals approach nearer to the spherical shape. This shifting is
greatest in the case of the second mode. This in conjunction with
the greatest breadth of the second curve in figure B is what would
be expected if the premise in regard to the effect of fixation discussed
above (page 251) is correct. Extra care was used in the fixation of
the latter lot of material whereas in the former only the ordinary pre-
cautions were taken. At any rate these differences between the two
groups do not detract from the evidence which they offer that there
are two distinct types of balantidia parasitic in pigs.
The value of these curves in showing race or species differentiation
is directly proportional to the extent to which any other factors which
258 University of California Publications in Zoology [VOL. 20
might produce a bimodal curve are non-operative. Factors involved
in faulty technique were eliminated as far as possible. Over the effect
of growth or age variation, however, the observer has no control. The
possibility of these variations producing such curves as the one above
is precluded by reference to the data from which the curves are con-
structed. Among the individual measurements recorded in Table I
it will be noted that there are small individuals measuring 27 X 50/x,
and others measuring 42 X 50/x; and that among the larger individ-
uals, some measure 50 X 120/*, and some, 90 X 150/x. Further study
of Table I shows that the two types are found among all sizes of
individuals; consequently the variation of body proportions repre-
sented by the graphs is not correlated with variations of size, and
probably not with the age or growth of the individuals.
That the variation could be accounted for by the occurrence of
fission seems unlikely. Individuals might continue to elongate until
binary fission occurred, and then by this process they might be
shortened and the body proportion changed. Two considerations
oppose this explanation. In figure A nearly equal numbers are of the
respective types; in figure B each example contained almost exclusively
one type of individual. In the former material very few dividing
individuals were found, while in the latter not a single individual was
seen in fission in either sample of material. But to accord with the
above explanation one would expect to find many dividing forms
among the elongate individuals represented by the broken line. In
the second place, if this explanation were valid one would expect
curves showing variation of body proportions to be continuous. Such
is not the case, as is shown in figures A and B where the curve is
bimodal due to a decided decrease of individuals having proportions
intermediate between the two types.
The possibility of any effect from gametic variation, was eliminated
by the study of conjugating forms, through which it was determined
that isogamy was the rule. Likewise the possibility of influence of
the quality of intestinal content of the host was eliminated by the
frequent occurrence of both types in the same host. Other factors it
would seem must be of minor importance and should give way for
more positively corroborative evidence which may be found in cor-
related morphological difference.
Other specific characters. In addition to the differences in relative
lengths of the axes, one notes a distinct difference in the points of
intersection, due to the variation in the shape of the types as pictured
1922] McDonald: On Balantidium coli and Balantidium suis 259
in figures D, E, F, G, and H. The one form resembles very closely
a hen's egg, the small end being anterior. In this case the longest
diameter crosses posterior to the midpoint of the longitudinal axis.
In the elongate type, usually the posterior end is as much drawn to
Figs. D-H. Camera lucicla drawings of Balantidium suis sp. nov. (figs. D
and E), and Balantidium coli (figs. F, G, and H), showing specific differences.
a point as is the anterior, and often more so. In these cases the longest
diameter intersects the longitudinal axis at or anterior to its midpoint.
Coincident with the taking of measurements a careful search was
made to detect other morphological differences which might occur
between the two forms and be of aid in distinguishing one from the
other. The earliest difference to be noted related to the macronucleus.
The macronucleus in the ovoid type is relatively short, being approxi-
mately !/3 the length of the entire organism. It is customarily bean-
shaped in appearance, but may be almost straight or so sharply bent
260 University of California Publications in Zoology [ V L. 20
at its middle as to form a short V (fig. I), and its width averages about
0.4 to 0.5 of its length. In. the slender types the macronucleus is rela-
tively long and slender, being approximately % of the entire length
of the organism. It is ordinarily sausage-shaped, but it may also be
in the form of a straight rod slightly enlarged toward the ends, or
it may be so curved as to form an almost complete ring. In contrast
to the form described above, the width in this case is about 0.2 to 0.3
of its length. Differences so great as these, viz., a length 2 to 3 times
the breadth in one case and 4 to 5 times the breadth in the other are
easily recognizable without actual measurement. These figures rep-
resent the average and do not mean that the limits of the two never
overlap. This difference in nuclei serves as one of the easiest and
surest ways of distinguishing the two types, for though the organism
during locomotion may modify its proportions tremendously this does
not noticeably affect the nucleus. It has been impossible to determine
any difference between the micronuclei of the two types.
A very noticeable difference concerns the relative position of the
cytostome. In the ovoid type the cytostome is almost, though never
quite, terminal (see figs. F, G, and H). As mentioned previously, the
anterior end is ordinarily drawn out to form a fairly decided point
which lies within the area enclosed by the adoral cilia. In the slender
type the cytostome is more laterally placed. The posterior limit of the
right lip of the cytostome may extend ventrally to a point % of the
length of the animal, in which case the dorsal portion of the adoral
circlet of cilia may pass approximately through the terminal point
of the body, but in normal form this point will never be within the
adoral area. The parts which make up the adoral region of the
animals show no fundamental differences except variation in the rela-
tive position of parts due to the lateral displacement of the cytostome.
For example, the plane of demarcation between ectoplasm and endo-
plasm, which is approximately vertical to the long axis of the animal
in the ovoid form, is at a decided angle, the ventral edge lying farther
posterior in the elongate forms (see figs. D and E).
In the opinion of some authors the ventral displacement of the
mouth is very significant (Delage and Herouard, 1896; Minchin,
1912). These authors believe that the ventral displacement of the
cytostome is progressive with evolution of the organism; i.e., that in
the more primitive types the cytostome is terminal while in advanced
groups it is successively displaced farther ventrally. Viewed in this
light, the position of the mouth is here of considerable significance as
1922] McDonald: On Balantidium coli and Balantidium suis 261
a specific character. Attempts to discriminate between the two forms
on the basis of cytopyge or vacuoles were without result.
The specific differences just discussed have seemed to indicate a
sufficient degree of separation of the two types to warrant iho~ division
of the ciliates of the genus Balantidium which occur in the pig into
two distinct species. The description by Malmsten (1857), in con-
junction with the figures (Malmsten, pi. 1, figs. 1-6) which he pub-
lished, make it practically certain that the ovoid type is the one
originally described by him and to which he gave the name Para-
moecium (?) coli.
So far as I have been able to determine, the elongate species above
described has never before been distinguished from Balantidium coli.
For this new species I suggest the name Balantidium suis. As a sum-
mary of the specific characters discussed above I give the following
Balantidium suis sp. nov. Body elongate; length approximately
twice the breadth and varies from 35 to 120/* ; breadth from 20 to 60/x ;
usually tapers more posteriorly, is blunter anteriorly, longest diameter
transects longitudinal axis anterior to its midpoint ; adoral region ven-
trally placed, cytostome % of way posteriorly along ventral surface;
nucleus rod or sausage-shaped, at least one-half the length of the entire
organism, its width about one-fourth of its length ; the species is para-
sitic in the pig.
The specific name, Balantidium suis, seemed fitting since it indi-
cated the common host, Su$ scrofa. Whether or not this species occurs
in man it has not been possible to determine conclusively. A review
of published case records of balantidiasis seems to show that it does
not, but only a few of these records are accompanied by figures or
descriptions of the organisms which are adequate for making positive
discrimination. Fortunately, I have been able in two cases to make
some direct observations.
Through the kindness of Mr. W. H. Barnes, of the Department of
Pathology of the University of California, I was permitted to study
sections of the human intestine which he had obtained at an autopsy
following a fatal attack of balantidiasis. Imbedded in the serous and
subserous layers were numerous balantidia. Measurements to show
proportions were of little value under the conditions, for the form
of each organism was largely determined by pressure, exerted by sur-
rounding tissues. But from other characters, the type of nucleus
especially, it was conclusively determined that the species there present
was Balantidium coli. No individuals of Balantidium suis were found.
262 University of California Publications in Zoology [ V OL. 20
Measurements of balantidia as they occur free in the human intes-
tine were made possible through the kindness of Dr. E. L. Walker,
of the Hooper Institute of Medical Research, who loaned me several
slides which he had prepared while in the Philippine Islands. This
material had been stained with haematoxylin. Using the same pre-
cautions as in previous work, a total of 100 individuals was measured.
The data were handled as before and the resulting graph is shown in
figure C. In comparison with previous graphs it will be noted that
this graph closely approaches coincidence with the curves representing
Balantidium coli, for its mode is at 1.3 while the extreme portion of
length and breadth is 1.5.
In addition to slides of human material, there was also loaned
material from one pig and from one monkey. It is interesting that
each showed a pure infection with Balantidium coli. The monkey
(Monkey No. 10, Table I; Walker, 1913) had been experimentally
infected by feeding it cysts from a pig, but not the pig from which
the above-mentioned material was taken. Therefore this material
yields no evidence regarding the validity of the specific differentiation
nor the possibility of Balantidium suis becoming established in mon-
keys or in man.
There is no likelihood of confusing the new species, Balantidium
suis with Balantidium minutum (Schaudinn, 1899). The differences
are very marked. The body of the latter is oval, pointed anteriorly,
more like Balantidium coli. The peristome reaches to the equatorial
plane. There is but a single vacuole while there are two in each of
the species considered here. The macronucleus is spherical, whereas
it is elongate in both Balantidium coli and Balantidium suis.
Balantidium coli (Malmsten) and Balantidium suis sp nov. are
ciliated protozoans, barely visible to the unaided eye, and are in a
general way sac-shape (balantidium, little bag). Viewed through the
microscope they appear grayish green in color. The homogeneity of
the cell contents is broken by the presence of the nuclei, the contractile
vacuoles, the food vacuoles, and sometimes by the presence of highly
refractile bodies, the paramylum bodies. The entire surface of the
body, except that of the oral plug, is covered with fine cilia. The cell
contents are retained by a thin transparent pellicle which is protective
1922] McDonald: On Balantidium coU and Balantidium suis 263
in function. The cytoplasm is distinctly differentiated into ectoplasm
and endoplasm. The former constitutes a thin layer just underneath
the pellicle and in it is situated the basal apparatus of the cilia. The
layer of ectoplasm thickens greatly at the anterior end of the animal,
to form, as it were, a matrix for the cytostome and its accessory appa-
ratus. Within the ectoplasm, but not set off from it by a sharp line
of demarcation, is the endoplasm. In the endoplasm are numerous
food inclusions, often present in the form, of starch or paramylum
bodies. The macronucleus and the micronucleus are also within it,
but seem to have no constant position in the cell. The .macronucleus
is either bean-shaped (as in Balantidium coli) or elongate and sausage-
shaped (as in Balantidium suis). There are two contractile vacuoles,
the larger being situated anteriorly and the smaller posteriorly. They
lie closely beneath or may be entirely surrounded by ectoplasm, thus
belonging really within that layer.
So far as can be determined the animals show no modification with
respect to a substratum, yet the lateral and posterior displacement of
the cytostome has lead to the designation of that side, toward which
displacement occurs, as ventral, and the opposite surface as dorsal.
This terminology is very nearly universal in the literature on Balan-
tidium, and the correlated terms of right and left are used in the
original description of the family Bursaridae (Stein, 1867) and the
genus Balantidium (Claparede and Lachmann, 1858). The dorsal
side may be somewhat more convex than the ventral ; this occurs not
infrequently in Balantidium suis, though, due to the plasticity of the
organism, this is by no means constant. No part of the body is differ-
entiated for skeletal purposes. The anal aperture or cytopyge is at
the posterior tip and may be present as an actual aperture or only
as an extreme thinning of the ectoplasm and pellicle at this point. In
connection with it there is usually a rectal vacuole which serves as a
storage reservoir for solid waste awaiting extrusion.
Pellicle. The entire body is covered by an extremely thin but
resistant pellicle (pel., figs. I and L). The pellicle seems to be some-
what thickened, as shown by a higher degree of refractibility, along
the margin of the lips of the cytostome where it turns in to form the
lining of the oesophagus and the groove in which the oral cilia are set ;
otherwise, it is nowhere noticeably specialized. It shows alternating
University of California Publications in Zoology E V L. 20
post. c. v
Pig. I. Balantidium ooli. Ventral view showing principal structures. The
adoral cilia, with exception of one at either side, are indicated by basal granules
only. The adoral membranelles are also represented solely by the basal apparatus.
Ectoplasm is shaded, and ciliary rootlets are shown on one side only. X 1250.
ad. oil., adoral cilia; ad. cil. /., adoral ciliary fiber; ad. mcmb., adoral membranelles;
ant. c. v., anterior contractile vacuole; bg., basal granule; bg. ad. cil., basal granules
of adoral cilia ; cil., cilia ; oil. r., ciliary rootlet ; dr. oes. /., circumoesophageal fiber ;
cytpg., eytopyge ; ect., ectoplasm ; enl. ad. cil. r., enlargement of adoral ciliary root-
let; end., endoplasm; gr. b., granular band of ectoplasm; long. /., longitudinal
fibers; moo., macronucleus ; mic., micronucleus ; mot., motorium; nuc.memb.,
nuclear membrane; oes., oesophagus; or.pl., oral plug; or.pl.f., oral plug fibers;
pel., pellicle ; per., margin of peristome ; post. c. v., posterior contractile vacuole ;
rad. /., radial fiber ; ret. v^ rectal vacuole.
1922] McDonald: On Balantidium coli and Balantidium suis 265
ridges and grooves, the cilia passing through the bottom of the latter,
but this condition is not due to longitudinal thickenings in the pellicle
itself, but to the fact that it is closely applied to the ectoplasm which
is thus furrowed. It can often be separated in " blisters 'J_ from the
ectoplasm by tannic acid or weak alcohol, and when thus removed it
shows regular longitudinal rows of perforations through which the
cilia pass out from the ectoplasm. In this condition its transparency
is very evident. The pellicle is not extremely impervious. For
instance, when the active animals are introduced into normal salt
ad. memb. _
dr. oes. f. II /
or. pi. f.
Fig. J. The neuromotor apparatus of the adoral region, anterior view. X 2000.
., adoral ciliary fiber; ad. memb., adoral membranelles ; ~bg.ad.cil., basal
granule of adoral eilia; dr. oes. f., circumoesophageal fiber; oytst., cytostome;
mot., motorium; or.pl., oral plug; or. pi. f., oral plug fibers; per., margin of peri-
solution plasmolysis takes place very quickly, and they present a
grotesque appearance as they swim about with several huge depres-
sions in their surfaces due to the shrinkage. Intra vitam stains such
as neutral red and Janus green also penetrate very quickly. Resist-
ance to pressure and mechanical change, however, is very marked, and
is due to its tenacity and flexibility, both of which qualities are shown
when the animal forces itself through an opening much smaller than
the normal diameter of its body (fig. K) and also by the extreme flat-
tening which it withstands under the increasing pressure of the cover-
glass when evaporation of the preparation is allowed. As previously
mentioned, these qualities indicate that the pellicle is protective and
retentive in function rather than supportive or skeletal.
266 University of California Publications in Zoology [ V L - 20
These organisms show remarkable mobility when observed under
conditions as nearly normal as possible. I have attempted to depict
something of this plasticity in figure K. As they travel amid the
debris in the intestinal contents, which has been removed with
them, a tendency to penetrate is much more noticeable than any
avoiding reaction. Instead of reversing the ciliary action, backing
away and taking a new direction as would paramaecia, the balantidia,
when they come in contact with a solid object, rather appty themselves
to the surface, round up, and seem to roll along it. After a moment
of such slow contortion, they may swim away in a new direction,
Fig. K. Diagrammatic illustration of the plasticity of the organism, resulting
in ability to pass through remarkably small openings.
determined by the direction of the anterior end. They avail them-
selves of the slightest opportunity to force their way through or
between any obstacles. The anterior end, especially the thickened
ectoplasmic portion, becomes at such times decidedly elongate and
conical (fig. K, 6). The cilia of this region beat spirally producing a
boring action as this anterior tip is protruded into any slight opening.
This action has in many instances been observed to cause two obstacles,
either of which was larger than the organism itself, to separate
sufficiently to allow it to pass between. The aperture need not be
one-half of the diameter of the animal for the latter will constrict
(fig. K, c) and the fluid contents flow through anteriorly as it
progresses, resembling the process of putting a bag of beans through
a small hole in a board. Throughout observations of the activity of
these organisms, one is impressed with their fitness for penetrating
the mucous lining of the intestine and the underlying tissues. Its
thigmotropic response, its boring action, and its extreme plasticity,
all seem to be adaptations for the function of penetration.
Ectoplasm. Immediately underneath the pellicle, the cytoplasm
is differentiated to form the ectoplasm (ect., fig. I; pi. 27, figs. 1-7).
The ectoplasmic layer, except at the anterior end, does not exceed two
1922] McDonald: On Balantidium coli and Balantidium suis 267
microns in thickness. The anterior end of the animal, that is, all
anterior to a transverse plane which would transect the body at a
point % to y 5 of the way to the posterior end, is composed entirely
of ectoplasm. In this cone-shaped area is located the cytostome and
a large part of the neuromotor apparatus. The protoplasniTof this
region seems to be homogeneously granular in fundamental structure..
It stains very deeply with haematoxylin ; so deeply in fact, that in
differentiation it is necessary to destain other parts of the body almost
completely before this part reaches a degree of transparency suitable
for study. With Mallory's connective tissue stain this region also
stains very densely, taking on both the brilliant red and the deep blue
elements of the stain, in different structures, as will be explained below.
This extensive thickening of the ectoplasm at the anterior end is clearly
shown in the figures by Leuckart (1861) and has been noted by nearly
all who have studied the animal more recently, but I have failed to
find any discussion of its significance. This same phenomenon occurs
in the Ophyroscolecidae, as pointed out by Sharp (1914) in his work
on Diplodinium and by Braune (1913) in Ophyroscolex. In these
cases the change seems to be correlated with the high degree of activity
and specialization of the anterior end of the animal ; in Diplodinium
in connection with its selective feeding, and in Balantidium in con-
nection with both feeding and activity of this entire region in pene-
trating the mucosa of the intestine. The centering of the neuromotor
apparatus in this region gives additional evidence in regard to this
question which will .be discussed further in connection with the de-
scription of that apparatus.
Throughout the entire investigation of the minute structure of this
animal, I have been unable to demonstrate the presence of any definite
plane of demarcation between endoplasm and ectoplasm, such as the
" ectoplasmic boundary layer" described by Sharp (1914) in Diplo-
dinium, and shown in plate IV, figure 3 of his paper. Many of the
fixed preparations used in the search for such a layer were sections
of the animal, treated as nearly as possible according to the technique
used by him and stained, as were his preparations, with Mallory 's con-
nective tissue stain. So far as it was possible for me to determine,
any sharp boundary line between ecto- and endoplasm is lacking. On
the contrary, they merge into one another and only in a general way
can it be said where one terminates and the other begins.
Prowazek (1913, fig. 2) describes, in Balantidium coll, "ein Art
von Zwischenmembran " which appears as wavy lines in optical sec-
268 University of California Publications in Zoology [VOL. 20
tion. According to his interpretation this "Querlinie" separates the
protoplasm of the cell body into two regions, the * * apical zone, ' ' which
I have described above as a thickening of the ectoplasm, and the rest
of the cell protoplasm. The extent of this * * Zwischenmembran " he
does not note, but his text figures (1 and 2) do not show it as extending
quite to the pellicle, but instead as stopping short of the pellicle at a
distance about equivalent to the thickness of the ectoplasm at that
point. This is significant in my interpretation of this region, namely,
that what appears as a continuous line or plane when viewed from
the side is in reality, as shown in cross-sections (pi. 27, figs. 6 and 7),
a set of diverging fibers. These fibers take origin from dark-staining
Fig. L. Portion of the peripheral region of a cross-section of Balantidium coli,
showing the structure of the ectoplasm and arrangement of cilia, somewhat dia-
grammatic. X 1500. b. ff., basal granule; oil., body-cilia; oil.r., ciliary rootlet;
end., endoplasm; gr. &., granular band of ectoplasm; hy. &., hyaline band of ecto-
plasm; pel., pellicle.
enlargements on the longitudinal fibers in the wall of the gullet and,
diverging, pass peripherally until they turn posteriorly at the very
inner edge of the thin layer of ectoplasm which covers the remainder
of the body (pi. 28, figs. 9-12). Even in lateral view careful focusing
will often show that the apparent ' ' membrane ' ' is really discontinuous,
showing breaks and irregularities as one focuses on different levels
and hence can not be considered as a true membrane. The arrange-
ment of these fibers will be described more exactly under the discussion
of the neuromotor apparatus.
The ectoplasm which constitutes a layer less than 3 microns in
thickness around the remainder of the periphery of the cell shows
a definite and somewhat complex structure. In tangential sections
of the surface, which are so thin that they do not include much of the
underlying endoplasm, one detects alternating light and dark longi-
tudinal spiral bands (gr.b., hy.b., fig. N). These bands are parallel
to the rows of cilia and very nearly equal in width. In cross-sections
(fig. L) they are seen to extend nearly, if not quite the full depth of
1922] McDonald: On Balantidium coli and Balantidium suis 269
the ectoplasm. As one follows these bands (or "stripes," as they are
named by Johnson (1893, in his work on 8 tent or) anteriorly they seem
to lose their distinctness when they become continuous with the apical
cone. In some individuals, however, one can follow them some distance
into this cone, but never is there the same degree of differentiation of
the two areas in this region.
In the living animals, which are often quite opaque due to inclu-
sions, it is nearly impossible to distinguish these longitudinal light and
dark bands. With neutral red the dark or granular band stains
faintly. With the haematoxylin stains used in thin sections of fixed
material the dark band seemed to be finely granular in fundamental
structure. The granularity in this case must be determined largely
by the general appearance and stainability, for the individual granules
are so small as to defy identification. There is no indication, however,
of alveolar structure, so that the term granular is probably the more
applicable and will be used to distinguish this from the light band.
The latter takes only faintly the stains used and seems hyaline in
structure. The granular bands lie directly beneath the ridges in the
cuticle which occur between the rows of cilia. Or more correctly,
the ridges on the surface of the animal are produced by the projection
of these granular bands outwardly beyond the hyaline bands. These
latter are directly beneath the grooves of the surface where the cilia
pass through the cuticle and attach with the basal granules which lie
in longitudinal rows; a single row in each hyaline band. The ciliary
rootlets (cil. r., figs. I and L) extending in from the basal granules
proceed diagonally inward and pass into the interior margin of the
Stein as early as 1876 pointed out these alternating dark and light
stripes in Stentor. To the granular and bright stripes, Biitschli
(1889) gave the names ' ' Riffenstreif en " and " Zwischenstreif en, "
respectively. Johnson (1893) gives a careful description of these
bands as they occur in Stentor coeruleus. He notes that they vary
greatly in width, and this is true in Balantidium; but both bands are
much narrower than in Stentor, the combined width of the two not
exceeding two microns. In Stentor coeruleus Johnson (1893) gives
the width of the granular band as 22/x and that of the bright band
as 7/x, these measurements being taken just under the adoral zone. It
is interesting to note that in Balantidium coli the granular band is also
slightly wider than the bright band. These bands become narrower
from the region of the greatest circumference of the animals toward
270 University of California Publications in Zoology [ VoL - 20
each end, which is comparable with the arrangement in Stentor,
though in the latter the narrowing must necessarily take place in the
posterior direction only. The above author mentions the branching
of stripes, but this does not occur in Balanticfrium so far as I have been
able to determine. As the bands pass posteriorly, however, they
become less distinctly differentiated and are hard to follow, and it
might be that further study with more intensive stains would reveal
a union in the region of convergence at the posterior end. More recent
work has added to the number of Heterotricha that show this sort of
differentiation of ectoplasm. Maier (1903) shows the striped nature
of this layer in Prorodon and Spirostomum, while Neresheimer (1903)
confirms the structure found by Johnson ( 1893 ) in Stentor. Schuberg
(1887) also indicates a comparable plan of structure in Bursar la.
The granular ridges of ectoplasm between the furrows in which the
anal cirri are situated in Euplotes patella, discovered by Yocom
(1918), may be comparable with the bands which occur in Hetero-
Cilia. The entire surface of Balanticbium coli, with the exception
of the oral plug, is thickly beset with cilia (cil., ador. c., fig. I). These
are of two kinds, viz., those which make up the adoral row of cilia
and which measure from 8 to 12/A in length, and those covering the
body, which vary from 4 to 6ju. Those covering the apical cone form
an intergradation between the two. On this surface the cilia which
occur immediately posterior to the adoral row are only slightly shorter-
and slightly more slender than the adoral cilia themselves. Passing
posteriorly they gradually become shorter and less cirrus-like until
they reach the base of the apical cone. Thence posteriorly they retain
the uniform size.
The body cilia are comparatively short and very slender. So small
are they in fact that to observe a single one is nearly impossible. In
slides prepared by the usual methods no stain remains in the cilia if
destaining is carried sufficiently far to differentiate other structures.
Iodine (Weigert's solution) gives a fairly satisfactory stain for tem-
porary mounts. The arrangement of cilia may be determined most
readily by using a heavier stain and then observing the distribution
of basal granules. Neutral red proves very satisfactory for this pur-
pose. The cilia occur in longitudinal, slightly spiral rows, following
the grooves between the ridges in the pellicle. These rows originate
immediately posterior to the groove in which the adoral cilia are set
and for a very short distance pass almost meridionally ; very soon,
1922] McDonald: On Balantidium coli and Balantidium suis 271
however, they turn toward the left, that is, in a counter-clockwise
direction when the animal is viewed from a point exactly in front.
They continue their spiral direction until almost to the posterior end
when they again follow a meridional path to their termination. In
passing the entire length of the body any single row of cilia twists to
the left approximately 120, or one-third the entire circumference.
Whether some rows terminate or become continuous with contiguous
rows before reaching the posterior tip of the animal, I have been
unable to determine, for both basal granules and granular bands
become very indistinct in this region even in the best preparations.
The number of rows was counted with difficulty in several cross-
sections from the equatorial regions of different animals, and it was
found to vary from about 60 in small individuals to 120 in larger ones.
No correlation between the variation in the number of rows of cilia
and the species of the animal could be determined, but this is possibly
due to the limitation of observation.
Basal apparatus. The cilia perforate the pellicle and attach to
the basal granules which lie immediately underneath (fig. L). The
latter are small and apparently spherical or oval. They stain very
deeply black or blue with haematoxylin. In the living animal they
are readily emphasized by the use of neutral red, and less so by Janus
green. In preparations stained with Mallory's connective tissue stain
these granules show brilliantly red with the acid fuchsin, as do the
other parts of the neuromotor apparatus and also the micronucleus.
Longitudinally the granules are so closely placed that it is impossible
to observe whether they are actually connected by a fibre. Cross-
sections show that the cilia of one row have no transverse connection
by any sort of stainable fiber with those of the next row. The rows
of basal granules lie close beneath the depression in the pellicle in
the hyaline or bright band of the ectoplasm. A ciliary rootlet (cil. r.,
figs. I and L) extends from each basal granule centrally toward the
endoplasm. It does not proceed in an exact radial line but rather
diagonally toward the right until it enters the granular band near
the inner surface of the latter. The ciliary rootlets in some cross-
sections appear to have an exactly radial direction. In such cases,
however, the granular band is somewhat diagonal in the opposite
direction. This variation is probably produced either by torsion of
the animal or by the direction of the effective beat of the cilia at the
instant of fixation. The diagonal direction of the rootlets is readily
detected in tangential sections. In focusing down through such a sec-
272 University of California Publications in Zoology [ V OL. 20
tion, the rootlet is invariably seen to run from the basal granule
toward the observer's right into the contiguous granular band on that
side. Thus, to avoid any confusion that might arise from the terms
right and left, in a cross-section of the animal viewed from the anterior
surface (such a view is shown in fig. L) the ciliary rootlets swerve in
the counter-clockwise direction and enter the granular band lying
immediately in that direction.
As the rootlet enters into the granular band it apparently enlarges
thus forming a secondary basal granule. In some cases this may stain
even more deeply than the basal granule itself, and appear as a definite
body somewhat elongated in the direction of the circumference of the
animal. It was thought at first that this might be the cross-section of
a longitudinal fiber or myoneme. But the study of numerous tan-
gential sections has failed to show the presence of any longitudinal
fiber within the granular band. The stainability varies greatly and
in preparations which have stained lightly the ciliary rootlets appear
to fray out and merge into the granular band, while still retaining
deeper color than the rest. Which interpretation is correct it is
difficult to say, but the latter seems the more probable, especially in
view of certain relations with the neuromotor apparatus which will
be discussed later.
Putter (1903) reproduces a figure from Studnicka (1899) showing
in a schematic way five types of attachment of the cilia with their
basal apparatus. Of these, two, at least, represent cases in which two
basal granules or a diplosome are present. Saguchi (1917) in his
studies on ciliated cells of Metazoa says in part regarding the basal
granules of certain ciliated cells from amphibian larvae, ' * With favor-
able staining the basal corpuscles appear as diplosome or dumbbell
shaped granules. One of these is situated at the upper the other at
the lower border of the cuticle." In Balantidium coli the arrange-
ment with respect to protoplasmic layers is quite different, though
the cilia seem to follow somewhat the same plan of structure even to
the presence of rootlets.
The most fruitful comparison may be made with the .basal appa-
ratus of cilia in Isotricha prostoma as described and pictured by
Braune (1913). In this organism he describes diplosomic structure
of the basal apparatus, in which the basal granule lies directly beneath
the pellicle. The cilia, however, extend beyond the basal granule into
the underlying layer the * * Zwischenschicht " of Eberlein, and ter-
minate in the "Grenzschicht" with a second granule, which upon
1922 J McDonald: On Balantidium coli and Balantidium suis 273
maceration remains attached to the basal end of the cilium. So the
basal apparatus in Balantidium coli even to the relative location of
the basal granules is almost identical with that in Isotricha prostoma.
In Balantidium, however, as mentioned above, the "Grenzschicht"
seems to be lacking. The comparison becomes more significant in view
of the fact that both ciliates are parasitic in the digestive tract of
mammals, and both are in much the same state with reference to
the degree of specialization and degeneration correlated with habits
of the parasitic mode of life. So that in general morphology they
seem to be more alike, though they are in separate orders, than do
Diplodinium ecaudatum and Balantidium coli, which are in separate
Locomotion is the chief function of the cilia except for those of
the adoral zone. The balantidia swim in approximately a straight
line and not in a spiral course as do paramoecia. They do, however,
rotate on their axis as they progress. This rotation is generally from
left to right, that is, in a counter-clockwise direction when viewed from
a point in front of the animal. A few instances of reversal of the
direction have been seen, but it is not at all common. The direction
of rotation, i.e., from left to right, seemed at first inexplicable, since
this was not compatible with the direction of the rows of cilia. The
rows of cilia, as described above, are comparable to the threads of a
left-hand screw. In order to penetrate, such a screw must be turned
in a clockwise direction (when viewed from the point, not from the
head). Such, also, is the direction of rotation, of balantidia which one
would expect to find if the arrangement of the cilia were the con-
trolling factor, but the rotation is in the reverse direction. In the
further study of the problem, I fortunately obtained some very thin
tangential sections of animals on which the fixative had acted so
quickly that the cilia were stopped instantly and left in the relative
positions assumed in normal ciliary action.
Figure N is a camera lucida drawing of such a section. By analysis
of the position of the cilia on this and other like sections, it was
possible to determine the complete cycle of a single cilium. This cycle
is diagrammatically represented in figures M and 0. Figure N
includes about two and one-half cj^cles of action as represented by
the waves. The dark portions are produced by the prostrate position
of the cilia at the termination of the effective stroke. The lighter
274 University of California Publications in Zoology t v L - 20
areas between are due to the fact that the cilia are recovering their
vertical position and hence are viewed very nearly endwise. The
position of consecutive cilia in any single row, from one point in a
wave to a similar point in a following wave will fairly represent the
successive positions taken by a single cilium in making one complete
cycle. Figure M was made in this way. The arrow represents the
long axis of the animal. From this diagram it is seen that the cilium
at the end of the effective stroke lies rather close to the surface of
the body and not along the row but decidedly to the left from it. In
Fig. M. Diagrammatic representation of the successive steps in one complete
beat of a cilium of Balantidium coli. It also illustrates the positions of the respec-
tive cilia of a single row between the points a and & in fig. M, at which points the
cilia are in a prostrate position at the end of their effective stroke. The arrow
indicates the long axis of the animal.
Fig. N. Tangential section of Balantidium coli. The cilia still retain respec-
tive positions which they had in the normal swimming movements of the organism.
Fig. O. Diagram illustrating the effect of the ciliary action in the rotation of
the organism. The arrow represents the long axis of the animal; ab., the direction
of the rows of cilia ; cd., the direction of effective stroke of a cilium attached
at the point of intersection of the three lines; the ellipse is described by the tip
of the cilium.
recovery it straightens up and passes anteriorly, thence to the right,
crossing the row, of which it is a part, at right angles. At this point
the cilium leans anteriorly only slightly from the vertical. The
effective beat is produced by the quick stroke of the cilium posteriorly
and to the left, and continues until the cilium has crossed the row again
and lies close to the surface and extends to the left as represented
by the position of the last cilium shown in figure M. According to
the classification given by Putter (1903), the movement of the cilia
of Balantidium would be called^ infundibular. As will be noted from
1922] McDonald: On Balantidium eoli <md Balantidium suis 275
figure 0, the funnel described by the complete beat .of the cilium
is somewhat irregular, the rim outlined by the tip of the cilium is
elliptical, and the base of the cilium, i.e., the neck of the funnel, is
not central but is situated below the anterior focus of the ellipse.
The ellipse described by the tip of the cilium lies in a plane which is
not parallel to the surface of the animal, but which approaches it
much more closely posteriorly. It was possible to corroborate the
action of the cilia in observations on the living material. The cilia of
the apical cone are somewhat larger than the other cilia of the body,
and are closely coordinated in their action. In balantidia which were
allowed to cool until action had slackened considerably, these cilia
were observed to make their effective stroke at a decided angle to the
rows of cilia. For instance, in the boring action in connection with
the process of penetration described above, these cilia will beat in an
almost exactly transverse direction, always from right to left. In
further corroboration of this interpretation of the movements of the
cilia is the fact that it explains the rotation of the animal during
progression. It will be seen from figure that the effective stroke
of any single cilium will be in the direction cd. This line crosses both
the arrow, representing the long axis of the animal, and the line a&,
representing the rows of cilia, making an angle of approximately
20 with the latter. That is, the line cd forms an angle with the arrow
on one side about equal to the angle on the opposite side made by the
line ah. It clearly follows that if the effective stroke is in the direction
cd then rotation will be from left to right and not vice versa as would
be the case if the cilia beat in the direction of the rows in which they
are arranged. The structure of the basal apparatus is significant in
view of the direction of the effective stroke of the cilia, viz., posteriorly
and to the left. The cross-section shown in figure L is viewed anter-
iorly and shows that the ciliary rootlet from each basal granule passes
to the right and enters the granular band on that side of the hyaline
band in which the basal granule lies. Without giving to the ciliary
rootlets any motor or skeletal function, it still seems logical that they
conform in a general way to the axis of the cilium, for the latter during
the greater part of its movement inclines to the posterior and left of
the row of which it is a constituent.
The peristome (per. fig. J) may be said to comprise all that part
of the organism which lies within the row of adoral cilia. In the
active animal it is variable in shape. At times it is almost round
while at other times it may become a mere slit or groove. In what
276 University of California Publications in Zoology [ V L - 20
seems to be its more normal proportions, however, it is approximately
pear-shaped with the stem end of the pear directed ventrally. In
Balantidium eoli the adoral zone commonly includes the most anterior
point or apex of the animal at least its dorsal margin passes through
this point. In Balantidium suis, the anterior tip of the animal lies
wholly outside of this zone, the latter having migrated too far ventrally
to include it.
The cytostome (cytst., fig. J) does not occupy the whole interior
of the peristome, but is situated at its ventral end. There is some
indication that this aperture may be completely closed by the oral
plug (or. pi., fig. I) which comprises the rest of the peristome within
the adoral row of cilia. This oral plug bears no cilia. It is exceed-
ingly mobile, adapting itself readily to the almost constantly changing
shape of the apical cone. It lies dorsal to the cytostome and is not
exactly bilaterally symmetrical since it is pushed somewhat to the left
to make room for the oesophagus. It extends inward, thinning as
it does so, until it terminates about the beginning of the endoplasm.
It is ectoplasmic, but very finely granular as compared with the rest
of the ectoplasm. Mallory's connective tissue stain ordinarily gives
it a decidedly bluish tinge with slight spots of red only where there
are certain neuromotor fibers. Its action in feeding is very hard to
follow, but its high degree .of mobility impresses one when watching
the activities of the organism, and may be demonstrated with fixed
material by its extreme protrusion (pi. 28, fig. 14). In addition to
this, the fact that it is intimately connected with the neuromotor
apparatus would indicate that it functions in selective feeding. The
oesophagus (oes., fig. I; pi. 27, figs. 48) beginning at the cytostome,
passes inwardly, not quite radially but swerving slightly to the right.
It may be followed definitely through the ectoplasm and for a very
short way into the endoplasm where it ends blindly. So far as I
have been able to determine, it is a uniform tube-like opening without
evident enlargements or constrictions. Prowazek (1913), however,
gives in part the following description, ". . . . es sehnt sich jedoch
nicht direct trichterformig in die Tiefe, da man von der drei scharfe
Konturen noch nachweisen kann (fig. 1)." While studying living
forms stained with neutral red, I have often observed specimens in
the exact position of the one shown by Prowazek (1913, p. 7, text
fig. 1). The lines shown by him were easily recognizable, deeply
stained with the neutral red, but I could interpret them only in the
following way. The most anterior line which he shows seems to be
1922] McDonald: On Balantidium coli and Balantidium suis 277
clearly the ventral lip of the peristome ; the second line was identical
with the deep staining motorium (fig. I) in the forms which I studied,
and the most posterior line seemed identical with the ring of enlarge-
ments on the rootlets of the adoral cilia which lie close about the
oesophagus. The margin of the peristome is slightly raised^ forming
a ridge or lip. This ridge is most pronounced from the midventral
point, dorsal along the right margin of the cytostome, but as it pro-
ceeds around it becomes rather inconspicuous and wholly disappears
on the left side. Thus the cytostome has the appearance of opening
under a ledge, the ledge formed by the lip of the right side.
The peristome is delimited by an almost complete spiral circlet of
cilia, the adoral cilia (ad. cil., fig. I). The exact point of origin of
the row is hard to determine but it is approximately at the ventral
edge of the peristome, i.e., on the ventral lip of the cytostome. From
here it proceeds in a sort of groove, along the right margin, around
the dorsal margin, and down the left margin of the peristome. A
short distance in advance of the ventral point, the row of adoral cilia
turns into the cytostome and continues in a spiral course down the
oesophagus ; entering at the left dorsal side and ending in the ventral
wall about halfway down. Thus these cilia in their entire course make
one complete left-hand spiral, beginning on the ventral lip, passing
around the peristome and down the oesophagus, terminating in its
Over the lip of the cytostome between the point where the adoral
cilia turn into the oesophagus and the midventral point where this
row of cilia has its origin, the longitudinal rows of body cilia turn in.
Each of these rows, of which there are ten or twelve altogether, con-
tinues down the oesophagus until it meets the row of adoral cilia.
Since this latter enters spirally, there is a ciliated patch on the ventral
wall of the funnel-shaped 'oesophagus which is roughly the shape of a
right triangle, the base of which is the lip of the cytostome. The
hypotenuse is the row of adoral cilia which makes an acute angle with
the longitudinal row of body cilia which enters in the mid line and
which represents the third side of the triangle.
The adoral cilia, except where they lie within the oesophagus, are
completely separate each from the other. This is easily verified by
watching their action especially in a disintegrating animal, or one
cooled to slow up ciliary movement, under which condition coordina-
tion is frequently interrupted, and a single cilium will be seen acting
independently of its neighbor. Additional evidence is to be found in
278 University of California* Publications in Zoology [VOL. 20
the individuality of each basal granule. There is no evidence of fusion
of granules, though adjoining granules are connected by a neuromotor
fiber. However, in the triangular area mentioned above, there is con-
siderable evidence that the cilia are united to form membranelles. It
is very difficult to watch the action of these cilia, and the above con-
clusion was reached largely through a study of fixed material. In
cross-sections (pi. 27, fig. 4) the cilia of the region seem to be very
close together and quite regularly to be connected by, or to form, a
sheet of almost transparent substance. The regularity of this occur-
rence would lead one to believe that it is the normal structure and not
due to entanglement of the cilia in foreign matter. In addition, the
basal granules of this region (pi. 27, figs. 4 and 5) do not stand out
separately, but are so closely packed that they give the appearance
of a single deeply stained mass. I have been unable to distinguish
separate granules in the inner portion of the area and it seems likely
that actual fusion of the granules may have occurred. The basal
apparatus of this region is so densely packed and takes stain so readily
that in certain views it may easily be mistaken for the motorium. As
a result, it seems plausible to interpret this area as the basal apparatus
of membranelles which lie in a plane transverse to the axis of the
oesophagus. If this region be interpreted as a primitive oral groove
or cytostome, a forerunner of such an elaborate arrangement as occurs
in Euplotes patella (Yocum, 1918) or in Stentor, then comparison is
very significant, for in the latter two the membranelles also run trans-
versely in the cytostome. The only difference, then, between these
organisms and Balantidium in this regard would be the difference in
shape and extent of the area.
The adoral cilia (ad. til., fig. I) are approximately double the
length of the body cilia, i.e., from 6/x to S/A in length or, in the very
large individuals, they may reach a maximum length of 10/x. In
fundamental structure they are like the body cilia, but the relative
position of parts is somewhat different. Immediately beneath the
pellicle each cilium bears a basal granule and from this a fiber con-
tinues inward which passes between the adoral plug and the surround-
ing ectoplasm. The sum of all the fibers from adoral cilia marks off
very distinctly the conical cytostomal region from the surrounding
ectoplasm. They seem to constitute the only partition between the
protoplasm of the two areas, for I have not been able to detect any
membrane in this region making a complete separation of the adoral
region from the rest of the apical cone. Where the fibers pass from
1922] McDonald: On Balantidium coli and Balantidium suis 279
the ectoplasm of this cone into the endoplasm, each bears an enlarge-
ment which stains very deeply. This enlargement is undoubtedly
homologous with the inner enlargements of the basal apparatus of
the body cilia for it bears the same relation to the basal granule and
the cilium. It is farther removed from the basal granule but it main-
tains exactly the same relation to the ectoplasm and endoplasm, that
is to say, in either case this enlargement lies in the plane between the
two. From each enlargement a radial fiber extends laterally along
the base of the apical cone to the periphery of the cell. The portion
of the ciliary rootlet which continues inward from this enlargement is
very distinct and may often be traced almost to the posterior end of
the animal (fig. I). In no instance has it been possible to demonstrate
any attachment or connection of the posterior ends of these rootlets.
They often cross near the center of the organism and then fade out,
becoming indistinguishable in the endoplasm. For a short distance
inward from the oesophagus they are so closely placed dorsally and
laterally that they form a kind of wall, but ventrally they are less
numerous and likely to be much shorter, so that the pseudo-wall is
not complete. It is sufficient, however, to direct the food for some
distance into the endoplasm. There is no such high degree of differ-
entiation here as Sharp (1914) found in the oesophagus of Diplo-
The homology of the adoral and body cilia is evidenced by the com-
plete series of gradations from the one to the other which exist in the
cilia of the apical cone (fig. I). The cilia which are proximal to the
adoral cilia are almost identical with them. They are slightly smaller,
but each has the basal granule beneath the pellicle, a fiber connecting
this with an enlargement at the plane of differentiation of ectoplasm
from endoplasm, and the rootlet extending posteriorly.- The inner en-
largement is much smaller and the ciliary rootlet shorter than those of
the adoral cilia. These enlargements are connected with the enlarge-
ments of the adoral cilia by the radial fibers mentioned above. Passing
posteriorly the cilia become progressively smaller, the basal granule
and the enlargement closer together (due to the approach of the trans-
verse plane of demarcation between ectoplasm and endoplasm to the
pellicle), and the ciliary rootlets become progressively shorter and less
distinct, until the cilia of the marginal area of the apical cone become
identical with the body cilia. This apical cone then shows us a com-
plete gradation of differentiation between the body cilia and the adoral
cilia, and proves their homology.
280 Umverstiy of California Publications in Zoology [VOL. 20
Feeding is the chief function of the adoral cilia. They are closely
coordinated in action, as is shown by the fact that in degenerating in-
dividuals they will beat in unison after other cilia beat only erratically
or have ceased entirely. Coordination is most pronounced in the cilia
of the left lip. The action of the adoral cilia produces a strong eddy
in the surrounding medium with the vortex of the eddy within the
peristome. In the above description it was noted that the right lip
projected slightly forming a ledge or bank. The current produced
by the cilia strikes against this ledge and solid objects are deflected
into the underlying cytostome. The natural rotation of the animal
on its longitudinal axis as described above aids in this process, for the
right lip thus acts as the blade of an auger. The food particles pass
down the oesophagus and collect at the inner end in a sort of droplet.
After several bits have been collected, the droplet begins its circulation
in the endoplasm as a food vacuole.
The closure of the cytostome in all probability is effected by the
oral plug. The latter is very mobile and contains fibers of the neuro-
motor apparatus. It has frequently been seen to project anteriorly
in a knoblike protrusion (pi. 28, fig. 14). This same phenomenon was
observed by Wising (1871). In view of its situation, its sensitivity,
and its mobility, it seems plausible to interpret it as an oral plug
with essentially the same function as the oral disk of Diplodinium
ecaudatum (Sharp, 1914).
The discharge of indigestible portions of the food takes place at
a constant point at the posterior end of the animal, the cytopyge (cyt.,
fig, I). It is an opening, however, only at the time of discharge.
At other times there is only a thinning of the cortical layer which can
be identified with comparative ease in fixed material. In the living
organism the process of defecation was frequently observed. The
undigested particles become segregated at the extreme posterior end
in a sort of vacuole, the rectal vacuole (ret. v., fig. I; pi. 28, fig. 13).
After this vacuole has become of considerable size (often filling one-
third of the cell in degenerating forms) the pellicle over the cytopyge
ruptures and the contents are discharged. The pellicle quickly forms
again closing the aperture, collection of indigestible particles in the
rectal vacuole continues, and the process is repeated.
The contractile vacuoles (post. c. v., ant. c. v., fig. I) are two in
number, usually situated on the dorsal side, one anteriorly, well up
toward the apical cone, the other in the posterior one-third of the
organism. There is a great deal of variation in their location in
different animals, though in the individual their situation seems to be
1922] McDonald: On Ealantidium coli and Balantidium suis 281
very constant, at least throughout the limit of possible observation.
These vacuoles seem clearly to originate within the ectoplasm. When
fully distended they encroach far upon the region of the endoplasm
and it becomes impossible to tell whether or not they are entirely sur-
rounded by ectoplasm ; but from their origin such might be suspected
to be the case. Also such is the case in many related forms, for
example, Diplodinium eodudatum (Sharp, 1914) and Euplotes patella
The pulsation of the vacuoles was observed in several instances
for a long period of time. The rate of pulsation varies considerably,
occurring as rapidly as once in every thirty seconds under some
conditions, while under others a complete cycle from discharge to
discharge occupies a period of five minutes. In degeneration the
pulsation is likely to be very much retarded or may cease entirely,
the vacuoles becoming enormously distended and breaking together
thus forming one large vacuole occupying fully one-half of the interior
of the organism. Following this the animal ruptures and disintegrates.
The observation of a considerable number of normal individuals has
shown the usual cycle to be as follows. At two points in the ectoplasm
small droplets of clear liquid appear. These increase in size and
become the vacuoles usually seen. Contributing vacuoles or channels
such as occur in Paramaecium have never been noted. When they have
reached sufficient size (10/x, to 15/* in diameter in the ordinary indi-
vidual), they change from their spherical shape and begin to bulge,
each on the side toward the other. These bulges elongate until they
meet at a midpoint. At this midpoint a new vacuole arises and into
it, through the channels thus formed, the two vacuoles discharge their
contents. This large middle vacuole almost immediately discharges
to the exterior through the pellicle, and at the same time the other
two vacuoles re-form. However, the discharge of the middle vacuole
may be delayed until the other two are well formed and then the
individual has three vacuoles present. This and other variations are
not uncommon and should be taken into account in the use of the
number of vacuoles as a basis for classification. Leuckart (1861)
described a third contractile vacuole though he did not give its rela-
tive position to the other two and he did not describe the process of
contraction. He reported that he had observed the vacuoles "drop-
like" through the cytoplasm and wandering from place to place.
Solojew (1901) described the two vacuoles and observed a canal con-
necting the two, but he did not explain its function in discharge of
282 University of California Publication* in Zoology [VOL. 20
Endoplasm. Within the ectoplasm the body is composed of the
endoplasm (end., pi. 27, figs. 7 and 8; pi. 28, figs. 9 to 12) and the
inclusions therein. The endoplasm is less dense than the ectoplasm
and more coarsely granular. It is quite fluid, having a fairly definite
circulation in the active organism. From the inner end of the
oesophagus the direction of flow is posteriorly along the ventral sur-
face dorsalward just before reaching the posterior end, thence an-
teriorly along the dorsal surface. Just as it reaches the ectoplasm
of the apical cone, it is deflected posteriorly down through the central
portion of the body dorsal to the rootlets of the adoral cilia. This
course can be followed readily by observing the circulation of the food
The food vacuoles are customarily globular and may contain starch
granules, bacteria, or indigestible particles, of the food of the host.
The ingestion of bacteria is probably abnormal since it seldom occurs
except when the number of bacteria in the medium has increased
greatly during incubation. The starch granules may occur in enor-
mous numbers especially when the host has recently been fed on grain.
Red blood cells have not been noted in any of the balantidia observed
during the work.
That Balantidium may be cannibalistic is the only possible in-
terpretation of several findings. In these instances small individuals
were lying within the endoplasm of extremely large individuals
(100 X 125/i) and were in a state of disintegration. The larger indi-
viduals were Balantidium coli in every case and the smaller may have
been Balantidium suis, for both species were present in the material ;
but disintegration of the latter had progressed so far that specific
identification was uncertain. The possibility of interpreting this
phenomena as sporulation, which was described by Walker (1909),
is precluded by the disintegration of the included organism and the
fact that the normal vegetative phase of the nuclei of the large indi-
vidual is unmodified. Further evidence is to be found in the fact
that never more than a single individual has been found inside
another, while sporulation would produce several.
Macronucleus. As is generally the case in ciliates, balantidia are
binucleate, having a large macronucleus and a small micronucleus.
The macronuclei of Balantidium coli and Balantidium suis are slightly
1922] McDonald: On Balantidium eoli and Balantidium suis 283
different with respect to size and proportions as noted above (page
259), but structurally they are so closely alike that one description
will suffice for both. The macronucleus (mac., fig. I, pi. 28, figs. 13
and 14) always lies in the endoplasm but otherwise is not^constant
in location. Immediately surrounding it is an area in which the endo-
plasm is less granular and less dense in appearance, due perhaps as
Yocom (1918) has suggested of Euplotes patella to more rapid oxida-
tion in this region. It is elongate and may be straight and rodlike
or it may be sharply bent into a horseshoe shape. In any case its
diameter increases toward either end, giving it something of a dumb-
bell shape. This constriction in the central region and enlargement
at each end is more marked in Balantidium coli than in Balantidium
suis. The nucleus is delimited by a definite nuclear membrane
(nuc. m., fig. I) which is especially apparent in material in which
the macronucleus has shrunk due to faulty technique. Within this
membrane are packed rather densely the masses of chromatin. The
chromatin never occurs in equal sized regular granules but rather in
unequal very irregular masses, sometimes of considerable size (1 to 2/x,
in greatest dimension). Often there is a sort of vacuolated area,
usually near one end of the macronucleus, which is free from chroma-
tin. The significance of this vacuolated area I could not determine.
It does not seem to be due to degeneration and is not related to any
phase of reproduction. It is in no way comparable to the ' ' reconstruc-
tion band" described by Griffin (1910) and by Yocom (1918) in
Euplotes worcesteri and Euplotes patella, respectively. The chromatin
stains black with haematoxylin so that the macronucleus is the most
conspicuous structure in a stained individual. When Mallory's con-
nective tissue stain is used, the macronucleus takes on an orange hue.
Micronucleus. The micronuclei (mic., fig. I) of both species of
Balantidium parasitic in pigs are exceedingly small, not exceeding
5/x. in diameter. In the resting or vegetative phase the micronucleus
is subspherical and its flattened side lies close against the nuclear
membrane of the macronucleus. It may even lie in a depression in
the macronucleus in which position it is scarcely distinguishable from
the granules of the latter. It is surrounded by a nuclear membrane
readily recognized when the micronucleus is undergoing mitosis. In
a few instances the chromatin has appeared indistinctly granular but
it is customarily so closely packed that it looks like a single solid mass.
284 University of California Publications in Zoology [ V L. 20
The term neuromotor apparatus denotes an integrated system of
fibers, with a coordinating center, which is present in some Protozoa,
and which is credited with the power of conductivity of nervous im-
pulses, and hence functions in the coordination of the motor organelles
of the cell. The term was first used for ciliates by Sharp (1914) in
his account of the structure of Diplodiniwm ccaudatum. Since then
it has been employed by Kofoid and Christiansen (1915), Kofoid
(1916) for flagellates, and by Yocom (1918) and by Taylor (1920)
in their studies of the morphology and behavior of Euplotes patella.
The neuromotor apparatus of Balantidium coli can scarcely be
considered apart from the motor organelles of the cell. To insure
clarity in the description and discussion which follows, the motor
organelles, previously described in some detail, will be briefly reviewed.
With the exception of the oral plug which surrounds the cytostome
the organism is thickly beset with cilia. Of these, the adoral cilia are
largest. They are distributed about the margin of the peristome in
a row which ends in the membranellar region in the ventral wall of
the oesophagus. The rootlets of these cilia are exceedingly long, reach-
ing well into the posterior third of the cell, where they end without
any connection or attachment. They have two enlargements, the first
being the basal granule which lies just beneath the pellicle, and the
second being located at the junction of ectoplasm and endoplasm.
The remainder of the cilia are arranged in longitudinal spiral rows.
The most anterior cilia of these rows, i.e., those nearest the adoral
cilia, are nearly as sturdy as the adoral cilia themselves. But, pro-
gressing -posteriorly in the rows, the cilia become continuously smaller
until they reach their minimum size at the base of the apical cone of
ectoplasm. Likewise the ciliary rootlets become shorter, and the dis-
tance between the basal granules and the secondary enlargements of
the rootlets becomes less and less as one approaches the base of the
apical cone. This is shown in figure I. The remainder of the way
posteriorly the cilia are of uniform size, and the secondary enlarge-
ment of the basal apparatus of each cilium is the termination of the
ciliary rootlet and lies in the granular band of ectoplasm near its
plane of junction with the endoplasm.
In Bala/ntidium coli five distinct parts constitute the complete
neuromotor apparatus, namely (1) a motorium or coordinating cen-
ter, embedded in the ectoplasm close by the oesophagus, and from it
fibers pass out to the oral plug and the motor organelles ; (2) a circum-
1922] McDonald: On Balantidium coli and Balantidium suis 285
oesophageal fiber, beginning and ending in the motorium and giving
off branches as it passes through the oral plug; (3) a fiber connecting
the adoral cilia and the cytostomal membranelles with the motorium ;
(4) the adoral ciliary rootlets passing posteriorly from the basal
granules of the adoral cilia, each bearing an enlargement where it
passes from ectoplasm into endoplasm, and finally ending without
attachment in the endoplasm of the cell; (5) the radial fibers taking
origin from the enlargements of the adoral ciliary rootlets and passing
radially to the ectoplasmic layer where they turn posteriorly into the
The motorium (mot., figs. I and J) when viewed in ventral aspect
has somewhat the appearance of a reversed letter J. It lies within
the ectoplasm of the apical cone, close to the ventral and right walls
of the oesophagus. The part of the motorium corresponding to the
vertical shaft of the J lies along the right wall of the oesophagus, and
its anterior terminus is situated just inside and slightly dorsal from
the point of origin of the right lip of the cytostome. The curved end
of the J is posterior and passes ventrally and anteriorly around the
oesophagus and ends close to the inner termination of the rows of
adoral cilia. In the middle region a sharp slit-like constriction is often
very conspicuous. It is with the part of the motorium anterior to this
constriction, that the circumoesophageal fiber and the adoral ciliary
fiber have their origin. The portion posterior to this constriction is
quite variable both in size and in stainability. This variation is very
suggestive of the behavior of the parabasal body of certain flagellates
as described by Kofoid and McCulloch (1916), Swezy (1916), Kofoid
and Swezy (1919). These authors have shown that the parabasal body
is not kinetic in function but instead is a reserve or reservoir of
material easily transformed into energy, which reservoir fluctuates
according to the physiological condition of the animal. No direct
evidence can here be advanced establishing such a function for this
posterior portion of the motorium, but the fact of its fluctuation in
volume and its variation in chemical nature (as shown by stains)
would lead one to suspect that such an interpretation is correct.
The oircumoesophag&al fiber (dr. oes. /., figs. I and J) takes origin
from the anterior extremity of the motorium and passes into the oral
plug. Its course is very close to the inner, i.e., oesophageal, surface
of the plug. It encircles the oesophagus completely but in the mem-
branellar area it becomes very hard to follow. Certain sections (pi. 27,
fig. 3), however, seem to show that it unites again with the motorium.
It is not a smooth fiber but bears irregular enlargements from which
286 University of California, Publications m Zoology [VOL. 20
fibers pass both posteriorly and anteriorly into the ectoplasmic mass
of the oral plug. These branches make no observable connections, but
seem to fade out in the ectoplasm. Morphological evidence would
indicate that this portion of the neuromotor apparatus is concerned
solely with the activities of the very mobile oral plug. The adoral
ciliary fiber (ad. cil. f., figs. I and J) also arises from the motorium.
This fiber attaches to the motorium just anterior to the constriction.
It passes directly to the basal granule of the first cilium of the adoral
row from which it passes on and makes connection with each of the
basal granules of the entire row. It turns inward following the row
of adoral cilia along the dorsal or left-hand margin of the membranelle
area. Here its course is exceedingly hard tq determine, but like the
circumoesophageal fiber, some sections seem to show its connection
with the posterior end of the motorium.
The remainder of the neuromotor system is not directly connected
with the motorium. The adoral ciliary rootlets (ad. cil. r., fig. I) pass
inward from the basal granules of the adoral cilia through the ecto-
plasm of the apical cone into the endoplasm and well into the posterior
third of the organism where they end, not abruptly but by fading out.
There is absolutely no indication of any attachment of their inner
ends. Just posterior to the middle of the cell there is usually a very
distinct crossing of the ciliary rootlets from the opposite sides of the
peristome. Each of these adoral ciliary rootlets bears a decided enlarge-
ment at the point where it passes from the ectoplasm into the endoplasm.
The aggregation of these enlargements gives the appearance in cross-
sections through this region (pi. 27, fig. 6) of a zone of large, deeply
staining granules about the oesophagus. Each of these enlargements
gives rise to a fiber which passes radially outward in a transverse
plane. These have been termed the radial fibers (rad. /., fig. J ; pi. 27,
fig. 6). Each of these radial fibers as it passes peripherally connects
with small enlargements of the rootlets of the cilia of the apical cone.
The rootlets of the cilia of the apical cone are like those of the adoral
cilia except that they shorten progressively as they near the periphery,
at which point they scarcely extend into the endoplasm at all, becom-
ing identical with those of body cilia. Since the radial fibers and the
enlargements of the ciliary rootlets lie in the plane of contact between
the ectoplasm and the endoplasm they very clearly mark the limit of
the two. At the periphery the radial fibers turn posteriorly and
become lost in the granular band. This last fact is very suggestive,
since the terminal enlargements of the rootlets of the body cilia lie in
these granular bands.
1922] McDonald: On Balantidium coli and Balantidium suis 287
It has not been possible to demonstrate a posterior continuation
of the radial fibers within the granular bands. If they do not continue
posteriorly, making connections with the enlargements of the rootlets
of the body cilia, then the logical alternative seems to be to attribute
the function of conductivity to the granular band of ectoplasm itself.
There must be some means of conduction of stimuli, for the body cilia
are concerted in their action, though not to so high a degree as in
the case of the cilia of the apical cone. Protoplasm is generally con-
ceded to have the power of conducting stimuli. So here in Balan-
tidium coli there seems to be a transition from conduction by the
undifferentiated protoplasm which serves as a- matrix for the ciliary
apparatus, to a condition in which there is a differentiation of the
protoplasm into fibers or strands to serve the purpose. Moreover, the
increasing degree of differentiation is directly correlated with the
increasingly high degree of coordination of the motor organelles.
It will be seen from the figures and the above description that
Balantidium coli is equipped with a notably integrated system of
fibers bearing such morphological relations as would make the assign-
ing to them of the function of coordination perfectly logical. The
motorium is connected directly only with the oral plug and the adoral
cilia. But through ciliary rootlets and the radial fibers all of the
cilia of the apical cone are in connection with the adoral cilia. And
if the function of conductivity may be attributed to the granular
bands of the ectoplasm, into which the radial fibers turn and become
lost to view, and in which the enlargements of the ciliary rootlets of
the body cilia lie, then all of the motor organelles of the organism are
reached by the neuromotor apparatus, and by it the coordination of
these organelles may be explained.
Attributing to the various fibers described above the quality of
conductivity and to the whole neuromotor apparatus the function of
coordination of all of the locomotor organs in swimming and feeding,
microdissection experiments carried on by Taylor (1920), we may
consider the functions of the various parts from that point of view.
The main role of the motorium is to act as a coordination center. The
circumoesophageal fiber would serve to correlate the movements of the
oral plug with those of the adoral cilia in feeding and in avoiding-
reactions. The ciliary rootlets and radial fibers make possible the
coordination of all of the locomotor organs in swimming and feeding,
and especially the cilia of the apical cone which are employed in the
boring movement of the organism.
288 University of California Publications in Zoology [ V O L - 20
Up to the present time systems of intracytoplasmic fibers and
accessory neuromotor masses comparable to that found in Balantidium
coli have been fully described in several flagellates and a few ciliates.
The very primitive type occurring in Naegleria gruberi (Schardinger)
has been described by Wilson (1916). Kofoid (1916) and Swezy
(1916) have made a critical comparative study of the motor systems
of those flagellates, in which the} 7 have been most carefully studied.
That there is a striking similarity in the neuromotor systems of flagel-
lates and ciliates is clearly pointed out by Yocom (1918).
Among the ciliates, intracytoplasmic fibers have been known for
some time and there have been several descriptions of them and several
conflicting views as to their function (Engelmann, 1880; Biitschli,
1889; Schuberg, 1891; Maier, 1903; Prowazek, 1903; Griffin, 1910;
Braune, 1913). Sharp (1914), however, was the first to describe fully
a completely integrated fibrillar system with a central neuromotor
mass, to which he applied the term neuromotor apparatus.
Of the neuromotor apparatus of ciliates that of Balantidium coli
is the third to be quite fully worked out. In 1914 Sharp described
the neuromotor apparatus of Diplodinium ecaudatum (Fiorentini).
This apparatus consists of six parts. The central motor mass, or
motorium, lies in the area of thickened ectoplasm at the anterior end
of the animal between the dorsal and adoral membranelle zones. A
fiber connects the motorium with the basal granules of the dorsal mem-
branelles, a branch from which runs along the base of the inner dorsal
lip. Another fiber connects the motorium with the basal granules of
the adoral membranelles. A set of opercular fibers leave the motorium
and pass along underneath the operculum. Lastly, the motorium has
a definite connection by means of a fiber with what Sharp called the
circumoesophageal ring. There is also a set of fibers in the wall of
the oesophagus, which he termed the oesophageal fibers, and which
he believed took their origin from the circumoesophageal ring. All of
these structures as well as the micronucleus Sharp found had an
affinity for the acid fuchsin when Mallory's connective tissue stain
In Euplotes patella (0. F. Miiller) the neuromotor apparatus, as
described by Yocom (1918), is made up of five distinct parts. The
1922] McDonald: On Balantidium coli and Balantidium suis 289
motorium is a somewhat bilobed mass and lies in the ectoplasm at
the anterior end of the organism close to the right anterior corner of
the triangular cytostome. From the left end of the motorium five
main longitudinal fibers pass posteriorly, diverging slightly, and each
joins with one of the five anal cirri. The exact relation of thes^ fibers
to the basal plates of anal cirri has been very carefully determined
by Taylor (1920). Leaving the right end of the motorium a fiber
passes to the membranelles of the adoral zone. Directly connected
with this fiber is the "sensory structure" of the anterior lip. Lastly,
there are dissociated fibers in connection with the frontal, ventral, and
marginal cirri. In Euplotes, as in Diplodinium, all parts of the
neuromotor apparatus as well as the micronucleus stain brilliant red
with acid fuchsin.
For facilitating comparison, it might be well to summarize briefly
the neuromotor apparatus of Balantidium coli, as described above.
It consists in this organism of five distinct divisions. The motorium
is a J-shaped mass situated in the thickened ectoplasm of the anterior
end of the animal close to the cytostome and oesophagus. From it
arises the circumoesophageal fiber, which gives off branches to the
oral plug. A second fiber takes its origin from the motorium and
connects with the basal granules of the adoral cilia. The adoral ciliary
rootlets pass inward from the basal granules of the adoral cilia, and
may extend well into the posterior third of the cell. The radial fibers
take their origin from enlargements of the adoral ciliary rootlets,
at the point where they enter the endoplasm. They pass outward
radially, making connection with the ciliary rootlets of the cilia of
the apical cone, and at the periphery turn posteriorly and cannot
be traced farther in the granular bands of the ectoplasm. As in the
previous forms just summarized, the neuromotor apparatus as well as
the micronucleus of Balantidium coli is selective for acid fuchsin.
Of the three examples of neuromotor systems so far fully worked
out and described, each represents a different order of the class
Ciliata: Diplodinium being of the order Oligotricha; Euplotes being
of the order Hypotricha ; and Balantidium being of the order Hetero-
tricha. Yet in spite of the diversity of forms there is a remarkable
similarity in the neuromotor system. The presence of a motorium is
common to all three. In each of the three organisms it is located at
the anterior end of the animal and lies wholly within the ectoplasm
near the cytostome. By means of fibers it is connected with a part
or all of the motor organelles of the animal. Another feature of the
290 University of California Publications in Zoology [VOL. 20
fibrillar portion of the apparatus common to all three forms is the
strand connecting the motorium with all of the* adoral cilia or mem-
branelles, as the case may be. Finally, the system, in all cases, shows
an affinity for acid fuchsin.
The circumoesophageal ring present in Diplodinium is represented
in Balanticbium by the circumoesophageal fiber running through the
oral plug. The oral plug forms the wall of the greater part of the
oesophagus, and the fiber lies very close to the oesophageal surface.
From this fiber there are given off fibers which pass both anteriorly
and posteriorly in the mass of the oral plug. These fibers are strik-
ingly similar in location to the oesophageal fibers, described by Sharp
(1914) in the wall of the oesophagus of Diplodinium and believed by
him to arise from the circumoesophageal ring. Sharp points out that
these fibers approach very close to the micronucleus though there was
no demonstrable connection with it. In Balantidium this possibility
is precluded by the shortness of the oesophagus which in no case
extends inward to a point anywhere near the micronucleus. At times
when the organism is viewed from the proper angle, the ciliary root-
lets of the adoral cilia may have the appearance of ending in the
proximity of the micronucleus and suggesting a connection with it.
No such connection exists, however, as may be readily demonstrated
in large numbers of whole mounts and still better in sections where
these rootlets may be traced far posterior to the micronucleus, passing
it some considerable distance away. In the vegetative phase, it is
certain that no structural connection exists between any part of the
neuromotor apparatus and the micronucleus.
Of the three neuromotor systems of ciliates here considered, that
of Balantidium is clearly the least centralized, though none the less
a unified structure. In Diplodinium all motor organelles connect
directly with the motorium, and in Euplotes the same is true of all
except the marginal cirri which have no connection whatever, whereas
in Balantidium only the adoral cilia have direct connection with the
motorium while the cilia of the apical cone (and those of the body,
too, if they have any connection whatever) are connected with it only
indirectly through the radial fibers and the rootlets of the adoral cilia.
This lesser degree of centralization of the neuromotor apparatus may
perhaps be explained by the lesser degree of specialization of locomotor
organelles. Whereas in Diplodinium the body is devoid of cilia and
the dorsal and adoral zones of membranelles are the sole motor organ-
elles, and in Euplotes the locomotor organelles are restricted to the
cytostomal membranelles and a few cirri on the ventral surface, in
1922] McDonald: On Balantidium coli and Balantidium suis 291
the case of Balantidium the entire organism, with the exception of
the oral plug, is covered with cilia. So the slightly lesser degree of
specialization in the neuromotor apparatus would be the logical expec-
tation if modification of intracytoplasmic structures is correlated
with modification of external structures with which they have~a~direct
connection or of which they form an integral part.
From the point of view of efficiency, also, the arrangement in
Balantidium is readily explainable. The locomotor activities of the
organism may be separated into three main sorts, swimming, feeding,
and boring, this last very likely being used in penetration of the
intestinal wall of the host. In swimming the coordination of the entire
locomotor apparatus is necessary. In feeding, and in boring, particu-
larly, the coordination of the adoral cilia with those of the apical cone
is extremely essential. Such coordination would be most effectively
brought about by a direct connection of the parts concerned, and this
direct connection is accomplished by the uniting of all of the rootlets
of the cilia of these two regions by means of the radial fibers, without
the interpolation of the motorium.
Throughout the above discussion the assumption of a neural func-
tion for the neuromotor apparatus, i.e., the power of conductivity of
stimuli resulting in coordination of parts, has been based on two
general types of evidence, morphological and experimental. The
chemical evidence, that is, the affinity for acid fuchsin, as presented
by Sharp (1914) for Diplodinium and by Yocom (1918) for Euplotes,
seems slightly less convincing in the case of Balantidmm. In the last
named organism not only does the micronucleus, which has no connec-
tion with the neuromotor apparatus, show an affinity for acid fuchsin
but so also do certain cytoplasmic inclusions, which if not food par-
ticles are at least undoubtedly concerned in some way with metabolism
and have no morphological relation to the neuromotor apparatus.
Yocom (1918) states that there is more of the orange G in the micro-
nucleus giving it a different shade from the parts of the neuromotor
apparatus in the case of Euplotes; but in Balantidmm I have been
unable to detect any such differentiation.
Morphological evidence for attributing neural function to the
neuromotor apparatus has been clearly presented by Yocom (1918)
in his discussion of the apparatus in Euplotes. The evidence found
in Bakmtidium is not strikingly different. There is in the latter
organism the same intricate relationship between the neuromotor
apparatus and the motor organelles. The most active cilia, i.e., the
adoral cilia, are directly connected by the adoral ciliary fiber with
292 University of California Publications in Zoology [VOL. 20
each other and with the motorium. The cilia of the apical cone are
connected with the adoral cilia by the radial fibers and so indirectly
with the motorium. In this case, however, coordination with the adoral
cilia is most essential and this corresponds with their intimate con-
nection. These morphological interrelations all point to a neural func-
tion for the neuromotor apparatus.
Very convincing experimental evidence of the neural function is
to be found in the results of Taylor's (1920) microdissection experi-
ments on Euplotes patella. In Euplotes there is a fiber connecting the
adoral membranelles with the motorium, and also a fiber connecting
each of the five anal cirri with it. In a series of experiments Taylor
severed various ones of these fibers and observed very carefully the
effect on the movements of the animal. He then compared these move-
ments with the normal movements which he had previously carefully
analyzed and classified. Severing of these fibers resulted in lack of
coordination of the parts thus disconnected and resulted in abnormal
movements. Incision made in other parts of the cell, but which did
not sever neuromotor fibers did not so result. In the words of the
author, "It is apparent, then, that the destruction of the motorium
or the severing of some or all of its attached fibers is alone accountable
for modification in the perfect and efficient coordination between the
series of membranelles and the anal cirri. We may, therefore, regard
these normal morphological relationships as conditioning the animal's
usual behavior both in creeping and in swimming."
The general occurrence among Protozoa of protoplasmic modifica-
tion to form organelles for locomotion, feeding, digestion, excretion,
and protection has been known almost as long as have the Protozoa
themselves. The functions of such organelles have not been difficult
to determine. One might equally well expect to find modifications
correlated with the conduction of stimuli, but the establishing of
neural function is not so easy. This difficulty in conjunction with the
traditional idea of the simplicity of the Protozoa has resulted in con-
servatism in crediting any intracellular structures with the function
of conductivity. The recent detailed morphological studies on Proto-
zoa and the experimental work of Taylor (1920), however, leave little
doubt regarding the matter. This account of the neuromotor appa-
ratus of Balantidium coU and Balantidium suis presents additional
evidence of the likelihood of a quite general occurrence, in the Pro-
tozoa, of intracytoplasmic specialization resulting in a more or less
integrated system for purposes of coordination.
1922] McDonald: On Balantidium coli and Balantidium suis 293
1. Pigs are very generally infected with balantidia as shown by
the findings in previous investigations, many of which were carried
on in foreign countries, and by the finding of 68 per cent infection
among the two hundred pigs examined during the present investi-
2. There are two species of the genus Balantidium that are para-
sitic in the intestinal tract of pigs, namely, Balantidium coli and
Balantidium suis (sp. nov.).
3. Balantidium coli is the species first described by Malmsten
(1857) from man, and later by Leuckart (1861) as a parasite in pigs.
4. Balantidium suis (sp. nov.) has not hitherto been distinguished
from Balantidium coli. The former differs from the latter in being
more elongate and being broadest anterior instead of posterior to the
equatorial plane; in having a more slenderly proportioned macro-
nucleus ; and in having the mouth displaced ventrally, instead of being
almost terminal, which causes the plane of demarcation between ecto-
plasm and endoplasm in this region to slant posteriorly toward the
ventral surface instead of being perpendicular to the longitudinal
axis, as is the case in Balantidium coli.
5. So far as recorded facts will justify conclusions, it seems un-
likely that Balantidium suis occurs as a parasite of man, but instead
that Balantidium coli is the cause of balantidiasis. Whether or not such
is the case, it is very desirable that the occurrence of the two species
in pigs be taken into account in future work on experimental infection,
for to a failure to distinguish between the two species may be due
the seemingly conflicting results of previous experiments.
6. The cilia of the two species are homologous. Variation occurs
in size and relative position of parts only. The basal apparatus is
essentially diplosomic, consisting of a basal granule connected by a
ciliary rootlet to a secondary enlargement. The former is situated just
beneath the pellicle ; the latter lies in the plane of demarcation between
ectoplasm and endoplasm. The adoral cilia are largest, the basal granule
and secondary enlargement are farthest removed from one another, as
the ectoplasmic thickening is greatest in this region, and the ciliary
rootlet may extend far into the endoplasm. The cilia of the apical
cone intergrade between the adoral cilia and the body cilia. As one
294 University of California Publications in Zoology [ VOL - 20
progresses posteriorly, they become smaller in size, the secondary
enlargement approaches the basal granule as the ectoplasmic layer
becomes thinner, and the extension of the rootlet into the endoplasm
becomes shorter. The body cilia are smallest and their rootlets
terminate in the secondary enlargement. The cilia of the anterior
end are highly concerted in action. They beat in such a way as to
give the animal a remarkable boring motion which probably serves
in the penetration of the mucosa of the intestine.
7. Both species possess a neuromotor system. This is a highly
developed and integrated system consisting of five correlated parts.
The motorium, lying within the ectoplasm near the cytostome, gives
rise to a circumoesophageal fiber. In addition, there is a heavier fiber
which connects it with the basal granules of the adoral cilia. The root-
lets of the adoral cilia extend far into the endoplasm, usually well into
the posterior one-third of the cell. Where they pass from ectoplasm
into endoplasm each adoral ciliary rootlet bears an enlargement and
from this arises a radial fiber which passes to the periphery, turns
posteriorly, and disappears in the granular band of ectoplasm. In
passing to the periphery these radial fibers connect with enlargements
of the rootlets of the cilia of the apical cone.
Transmitted February 26, 1921.
Zoological Laboratory, University of California,
1922] McDonald: On Balantidium coli and Balantidium suis 295
BEL, G. S., and COURET, M.
1910. Balantidium coli infection in man. Jour. Infect. Dis., 7, 609-624, 4 pis.
1904. Ueber Infusorien aus asiatischen Anuren. Arch. f. Prot., 3, 138-174,
pi. 1, 23 figs, in text.
BOECK, W. C.
1917o. Mitosis in Giardia microti. Univ. Calif. Publ. ZooL, 18, 1-26, pi. 1.
1917&. A rapid method for the detection of protozoan cysts in mammalian
faeces. Ibid., 18, 145-149.
1913. Untersuchungen iiber die im Wiederkauermagen vorkommenden Proto-
zoan. Arch. f. Prot., 32, 5-63, pis. 3-6.
1909. Demonstration du role pathogene du Balantidium coli. C.-R. Soc. Biol.,
Paris, 67, 103.
1889. "Ciliata" in "Protozoa" (1887-1889) in Bronn, Klass. und Ordn. des
Thierreichs, 1, (3), 1228-1841, pis. 56-86.
1911. tiber die zyklischen Variationen des Caryosomes bei zwei Arten para-
sitischer Cilia ten. Mem. Inst. Oswaldo Cruz, 3, 136-144, 2 pis.
CLAPAREDE, E., and LACHMANN, J.
1858. Etudes sur les infusoires et les rhizopodesi. (Geneve, Kossmann), 1,
247-248, pi. 13.
DELAGE, Y., and HEROUARD, E.
1896. Traite de zoologie concrete. (Paris, Schleichter Freres), 1, 582, 870
figs, in text. Eef. footnote, 404, fig. 692.
DOBELL, C. C.
1909. Researches on the intestinal Protozoa of frogs and toads. Quart. Jour.
Micr. Sci, 53, 201-277, 4 pis.
1911. Lehrbuch der Protozoenkunde. (Jena, Fischer), ed. 3, xii+1043, 951
figs, in text.
EHRENBERG, C. G.
1838. Die Infusionsthierchen als volkommene Organismen. (Leipzig, Voss),
xviii + 547 ; Atlas, pis. 1-64.
ENGLEMANN, T. W.
1880. Zur Anatomic und Physiologic der Flimmerzellen. Pfliiger's Arch. ges.
Physiol., 23, 505-535, pL 5.
GRIFFIN, L. E.
1910. Euplotes worcesteri sp. nov., I, Structure. Philippine Jour. Sci., 5,
291-312, pis. 1-3, 13 figs, in text.
JENNINGS, H. S.
1908. Heredity, variation and evolution in Protozoa. Proc. Am. Phil. Soc.,
296 University of California Publications in Zoology IT OL - 20
JOHNSON, H. P.
1893. A contribution to the morphology and biology of the stentors. Jour.
Morph., 8, 467-562, pis. 23-24.
KOFOID, C. A., and CHRISTIANSEN, E. B.
1915. On binary and multiple fission in Giardia muris (Grassi). Univ. Calif.
Publ. Zool., 16, 30-54, pis. 5-8, 1 fig. in text.
KOFOID, C. A., and McCuLLOCH, I.
1916. On Trypanosoma triatomae, a new flagellate from a hemipteran bug
from the nests of the wood rat Neotoma fuscipes. Ibid., 16, 113-126,
KOFOID, C. A., and SWEZY, O.
1915. Mitosis and multiple fission in triehomonad flagellates. Proc. Am. Acad.
Arts and Sei., 51, 289-378, pis. 1-8, 7 figs, in text.
1919. On Trichonympha campanula nov. sp. Univ. Calif. Publ. Zool., 20,
41-98, pis. 5-12, 4 figs, in text.
LEEUWENHOEK, A. VON.
1708. "Animalcula e stercore ranarum." Opera omnia, 2, 49-64.
1861. Paramoecium ooli. Wiegemann's Archiv, 1, 80, pi. 5.
LONG, J. A.
1912. Studies on early stages of development in rats and mica Univ. Calif.
Publ. Zool., 9, 105-136, pis. 13-17, 11 figs, in text,
MAIER, H. N.
1903. Ueber den feineren Bau der Wimperapparate der Infusorien. Arch. f.
Prot, 2, 73-179, pis. 3-4.
MALMSTEN, P. H.
1857. Infusorien als Intestinaltiere beim Menschen. Virchow Arch. f. pathol.
Anat., 12, 302-309, pi. 10.
1883. Contribution a 1 'etude morphologique et anatonlique des infusoires
cilies. Arch. Zool. Exp. et Gen., (2), 1, 427-664, pis. 19-24.
METCALF, M, M.
1908. Opalina anatomy and reproduction. Arch. f. Prot., 13, 195-375, pis.
MlNCHIN, E. A.
1912. An introduction to the study of the Protozoa. (London, Arnold),
xi + 520, 194 figs, in text.
NERESHEIMER, E. E.
1903. Die Hohe histologischer Differenzierung bei heterotrichen Ciliaten.
Arch. f. Prot., 2, 305-324, pi. 7, 1 fig. in text.
VON PROWAZEK, S.
1903. Flagellatenstudien ; Anhang; fibrillare Strukturen der Vorticellen.
Ibid., 2, 195-212, 2 pis.
1913. Zur Kenntnis der Balantidiosis. Arch. f. Schiffs-u. Tropenhyg., 17,
369-390, 2 pis., 9 figs, in text.
1903. Die Flimmerbewegung. Ergebn. d. Physiol., 2, 1-102, 15 figs, in text.
1917. Studies on ciliated cells. Jour. Morph., 29, 217-268, pis. 1-4, 1 fig. in
1922] McDonald: On Balantidium coU and Balantidium suis 297
SGHAUDINN, F., and JAKOBY, M.
1899. Ueber zwei neue Infusorien im Darm des Menschen. Centralbl. f.
Bakt., Abt. I, 25, 487-494, 4 figs, in text.
1886. Ueber der Bau der Bursaria truncatella mit besonderer Berucksichti-
gung der protoplasmatischen Structuren. Morph. Jahrb., 12, 333-
365, pis. 19-20.
1891. Ueber einige Organizationsverhaltnisse der Infusorien. des Wieder-
kauermagens. Sitz.-ber. d. phys.-med. Ges. Wurzburg, 1891, 122-137.
1900. Parasitische Wimperinfusorien (Endoparasiten). Arb. der St. Peters-
burger naturf. Gesellsch., 29, 1-135, pis. 1-2.
SHARP, E. G.
1914. Diplodinium ecaudatum, with an account of its neuromotor apparatus.
Univ. Calif. Publ. Zool., 13, 43-122, pis. 3-7, 4 figs, in text.
SOLO JEW, N. S.
1901. Das Balantidium ooli als Erreger chronischer Durchfalle. Centralbl. f.
Bakt., 29, 321-830; 849-860, 8 figs, in text.
1867. Der Organismus der Infusionsthiere nach eigenen Forschungen in sys-
tematischer Eeihenfolge bearbeitet. (2) Naturgeschichte der heter-
otriehen Infusorien (Leipzig, Englemann), viii + 355, 16 pis.
STRONG, E. P.
1904. The clinical and pathological significance of Balantidium coll. Bureau
Gov't. Labs. (Manila, P. I.), Bull. 26, 77, 10 pis.
1916. The kinetonucleus of flagellates and the binuclear theory of Hartmann.
Univ. Calif. Publ. Zool., 16, 185-240, 58 figs, in text.
TAYLOR, C. V.
1920. Demonstration of the function of the neuromotor apparatus in Euplotes
by the method of microdissection. Ibid., 19, 403-470, pis. 29-33, 2
figs, in text.
1904. Ueber den feineren Bau von Didinium nasutum O. F. M. Arch. f. Prot.,
5, 281-321, pis. 12-13, 3 figs, in text..
WALKER, E. L.
1909. Sporulation in the parasitic Ciliata. Ibid., 17, 297-306, 2 pis.
1913. Experimental balantidiasis. Philippine Jour. Sci., 8, (B), 333-349, 7
WILSON, C. W. v
1916. On the life history of a soil amoeba. Univ. Calif. Publ. Zool., 16, 241-
292, pis. 18-23.
WISING, P. J.
1871. Till kannedomen om Balantidium coli hos manniskan. Nordiskt Med.
Ark., 3, 1-30, 1 pi.
YOCOM, H. B.
1918. The neuromotor apparatus of Euplotes patella. Univ. Calif. Publ.
Zool., 18, 337-396, pis. 14-16, 1 fig. in text.
EXPLANATION OF PLATES
Camera lucida drawings of a series of transverse sections of Balantidium coli
(Malmsten). The series begins at the anterior end and progresses posteriorly
about one-third the length of the organism. X 1000.
Fig. 1. This section shows dorsal portion only of peristome. The adoral cilia
are removed showing their basal granules clearly.
Fig. 2. A portion of the oral plug is shown with the circumoesophageal fiber
and the connected oral plug fibers. The deeply-staining region between proto-
plasm of oral plug and the surrounding ectoplasm, so marked in this individual,
is rarely found.
Fig. 3. The continuation of cilia over the ventral lip and down into the cyto-
stome are to be noted particularly; the beginning of the motorium on the
(reader's) left of the cytostome; and the connection of the adoral ciliary fiber
with the motorium.
Fig. 4. In this figure the cilia of the cytostome give the appearance of mem-
branelles; the circumoesophageal fiber makes connection with the motorium.
Fig. 5. This shows the beginnings of the enlargements of the adoral ciliary
Fig. 6. Here the oesophagus is completely surrounded by the enlargements
and radial fibers may be seen arising from some of them.
Fig. 7. The extreme posterior tip of the motorium appears within the circle
of enlargements; the dorsal half of this section is through the endoplasm.
Fig. 8. This section is posterior to the adoral apparatus with the exception of
the rootlets of the adoral cilia which in cross-section can not be distinguished from
the granules of the endoplasm.
UNIV. CALIF. PUBL. ZOOL. VOL. 20
[ MCDONALD ] PLATE 27
Figs. 9-12. Series of longitudinal sections through the anterior end of Balan-
tidium ooli (Malmsten). X 1000. These sections are oblique, being more nearly
frontal than sagittal, however. The section shown in figure 9 is tangential to the
margin of the peristome some distance to the right of the most dorsal point of the
latter (see fig. J in text). The remainder progress toward the left ventral lip.
The oral plug fibers, the radial fibers, and the adoral ciliary rootlets are shown
clearly in these sections.
Fig. 13. A sagittal section through Balantidium suis (sp. nov.). X 1000.
The specific characters, viz., elongate body and macronucleus, and oblique plane
delimiting apical cone of ectoplasm, are shown in this section. The cytopyge is
distinct and open to the exterior. A paramylum body of considerable size is
present in the endoplasm.
Fig. 14. An oblique longitudinal section through Balantidium coli (Malmsten)
showing the protrusion of the oral plug. X 750.
UNIV. CALIF. PUBL. ZOOL. VOL. 20
[ MCDONALD ] PLATE. 28
lf --t- ;
UNIVERSITY OF CALIFORNIA PUBLICATIONS (Continued)
16. The Subclavian Vein and Its Relations in Elasmobranch Fishes, by J. Frank
Daniel. Pp. 479-484, 2 figures in text. August, 1918 . ......... ... .. ......... ----- ...... 1"
17 The Cercaria of the Japanese Blood Fluke, Schistosoma japomcum Katsu-
rada, by William W. Cort. Pp. 485-507, 3 figures in text.
18. Notes on the Eggs and Miracidia of the Human Schistosomes, by William
W. Cort. Pp. 509-519, 7 figures in text.
Nos. 17 and 18 in one cover. January, 1919 ......................................... *
Index, pp. 521-529.
Vol 19. 1. Reaction of Various Plankton Animals with Reference to Their Diurnal
Migrations, by Calvin O. Esterly. Pp. 1-83. April, 1919 .. ....... .......... _ .85
2. The Pteropod Desmoptcrus pacificus (sp. nov.), by Christine Essenberg. Pp.
85-88, 2 figures in text. May, 1919 ................ - ..................... ------.- ..... -----;-""--- * 05
3. Studies on Giardia microti, by William C. Boeck. Pp. 85-136, plate 1, 19
figures in text. April, 1919 ............. .... ......... .......................... - ................. ---- ' b
4 A Comparison of the Life Cycle of Crimdia with that of Trypanosoma in
the Invertebrate Host, by Irene McCulloch. Pp. 135-190, plates 2-6, 3
figures in text. October, 1919 .......... ~ ...... - .......................................... V"'"-^V""^
5 A Muscid Larva of the San Francisco Bay Region Which Sucks the Blood
of Nestling Birds, by O. E. Plath. Pp. 191-200. February 1919 .10
6 Binary Fission in Collodictyon triciliatum: Carter, by Robert Clinton Rhodes.
Pp 201-274, plates 7-14, 4 figures in text. December, 1919 ....................... ... 91-00
7. The Excretory System of a Stylet Cercaria, by William W. Cort. Pp. 275-
281, 1 figure in text. August, 1919 . .......................................... - ..... -""""""""" * 1U
8. A New Distome from Eana aurora, by William W. Cort. Pp. 283-298, 5
figures in text. November, 1919 ............ . ..................................... ............ --- ..... f<2
9 The Occurrence of a Rock-boring Isopod along the Shore of San Francisco
Bay, California, by Albert L. Barrows. Pp. 299-316, plates 15-17. De- ^
10. A C N n ew e MorphoioScarint"erp7etation of the Structure of Noc'iiluca, and Its
Bearing on the Status of the Cystofiagellata (Haeckel), by Charles A.
Kofoid. Pp. 317-334, plate 18, 2 figures in text. February, 1920 ... ......... .25
11 The Life Cycle of Echinostoma revolutum (Froelich), by John C. Johnson.
Pp. 338-388, plates 19-25, 1 figure in text. May, 1920 ........... ........
12 On Some New Myriopods Collected in India in 1916 by C. A. Kofoid, by
Ralph V. Chamberlin. Pp. 389-402, plates 26-28. August, 1920 ... .20
13. Demonstration of the Function of the Neuromotor Apparatus in ^fo**
by the Method of Microdissection, by Charles V. Taylor. Pp. 403-470,
plates 29-33, 2 figures in text. October, 1920 .................. . ................................ 85
Index In preparation.
Vol.20. 1. Studies on the Parasites of the Termites. I. On StreWomasUx strix, a Poly-
mastigote Flagellate with a Linear Plasmodial Phase, by Charles Atwood
Kofoid and Olive Swezy. Pp. 1-20, plates 1-2, 1 figure in text. July, 1919 .25
2. Studies on the Parasites of the Termites. II. On TricJwmitus termitidis, a
Polymastigote Flagellate with a Highly Developed Neuromotor System,
by Charles Atwood Kofoid and Olive Swezy. Pp. 21-40, plates 3-4, 2
figures in text. July, 1919 ................. _ ......................................... -- ....... - ........... -- ?
3 Studies on the Parasites of the Termites. III. On TrichonympTia campanula
sp. nov., by Charles Atwood Kofoid and Olive Swezy. Pp. 41-98, plates
5-12, 4 figures in text. July, 1919 ........ ..... ........... ......
4. Studies on the Parasites of the Termites. IV. On Leidyopsis sp en ? en /
nov. sp. nov., by Charles Atwood Kofoid and Olive Swezy. Pp. 99-116,
plates 13-14, 1 figure in text. July, 1919 ..... .............
5. On the Morphology and Mitosis of Cliilomastix meswh (Wenyon), a
Flagellate of the Human Intestine, by Charles A. Kofoid and Olive Swezy.
Pp. 117-144, plates 15-17, 2 figures in text. April, 1920 . ....... -35
6. A Critical Review of the Nomenclature of Human Intestinal Flagella ;es,
Cercomonas, CMornaistix, Trichomonas, and Giardia, by Charles A. Kofoid.
Pp. 145-168, 9 figures in text. June, 1920 ..... ................................. -----
7. On the Free, Encysted, and Budding Stages of Councilmania la-fteun a Para-
sitic Amoeba of the Human Intestine, by Charles Atwood Kofoid and
Olive Swezy. Pp. 169-198, plates 18-22, 3 figures in text. June, 192 .60
8. Mitosis and Fission in the Active and Encysted Phases of Giardia entenca
(Grassi) of Man, with a Discussion of the Method of Origin of Bilateral
Symmetry in the Polymastigote FlageUates, by Charles A. Kofoid and
Olive Swezy. Pp. 199-234, plates 23-26, 11 figures in text. March,
9. The Micro-injection"of" "Paramaecium, by Chas. Wm. Rees. Pp. 235-242.
10 Onaittttdm~wr^ and Balantidium suis (sp. nov.), wth
an account of their neuromotor apparatus, by J. Daley McDonald.
Pp 243-300, plates 27, 28, 15 figures in text. May, 1922 .............................. 1.00
UNIVERSITY OF CALIFORNIA PUBLICATIONS (Continued)
11. Mitosis in Endamoeba dysenteriae ia the Bone Marrow in Arthritis de-
formans, by Charles Atwood Kofoid and Olive Swezy. Pp. 301-307,
7 figures in text.
12. Endamoeba dysenteriae in the Lymph Glands of Man in Hodgkin's Disease,
by Charles A. Kofoid, Luther M. Boyers, M.D., and Olive Swezy. Pp. 309-
312, 4 figures in text.
Nos. 11 and 12 in one cover. April, 1922 .25
VoL 21. 1. A Revision of the Microtus calif ornicus Group of Meadow Mice, by Reming-
ton Kellogg. Pp. 1-42, 1 figure in text. December, 1918 50
2. Five New Five-Toed Kangaroo Rats from California, by Joseph GrinneU.
Pp. 43-47. March, 1919 05
3. Notes on the Natural History of the Bushy-tailed Wood Rats of California,
by Joseph Dixon. Pp. 49-74, plates 1-3, 3 figures in text. December, 1919 .25
4. Revision of the Avian Genus Passerella, with Special Reference to the Dis-
tribution and Migration of the Races in California, by H. S. Swarth. Pp.
76-224, plates 4-7, 30 figures in text. September, 1920 $1.75
5. A Study of the California Jumping Mice of the Genus Zapus, by A. Brazier
HowelL Pp. 225-238, 1 figure in text. May, 1920 _ 15
6. Two New Rodents (Genera Thomomys and Marmota) from the Eastern
Border of California, by Joseph Grinnell. Pp. 239-244, 6 figures in text,
November, 1921 15
7. A Study of the Calif ornian Forms of the Microtus montanus Group of
Meadow Mice, by Remington Kellogg. Pp. 245-274, 25 figures in text.
8. A Synopsis of the Microtus mordax Group of Meadow Mice in California,
by Remington Kellogg. Pp. 275-302, plate 8, 29 figures in text.
Nos. 7 and 8 in one cover. April, 1922 75
Vol. 22. 1. A Quantitative and Statistical Study of the Plankton of the San Joaquin
River and Its Tributaries in and near Stockton, California, in 1913, by
Winfred Emory Allen. Pp. 1-292, plates 1-12, 1 figure in text. June, 1920. $3.00
Vol.23. The Marine Decapod Crustacea of California, by Waldo L. Schmitt. Pp.
1-470, plates 1-50, 165 figures in text. May, 1921 5.00
UNIVERSITY OF CALIFORNIA LIBRARY