410 Prof. H. James-Clark on the Anatomy and 
p- 348, taf. xiii. figs. 1-5, eg), 1s an optical illusion! It was 
almost by accident that we were induced to doubt the character 
of this seemingly definite body. After having successfully fol- 
lowed two rows of cilia from the stem of the rotatory organ into 
and to the very bottom of the vestibule of an Hpistylis (E. galea, 
Ehr. ?), it seemed very strange that the “ bristle of Lachmann ” 
had not been met with during such a close and searching 
scrutiny. Recalling its position, as described by Lachmann and 
by Claparéde, and as we thought we had seen it on former 
occasions, it was observed that, whilst one of the rows of cilia, 
which had just been traced into the vestibule, occupied its right 
side, the other row was in the position of the so-called bristle ; 
i.e. it trended along the left side of the vestibule. Occasionally 
it was noticed that both the right and left rows of cilia had the 
appearance of single vibratory lashes, and that the left row, 
where it ran out beyond the aperture of the vestibule and 
thence upon the stem of the rotatory organ, had a particularly 
strong resemblance to a single lash or bristle, especially when 
the cilia projected toward the eye, so as to foreshorten the whole 
row. In the latter case it 1s easy to see how, when the cilia 
vibrated in regular succession, they would produce the effect of 
ai undulating line. The closest scrutiny with a Tolles one- 
eighth-of-an-inch objective and a B ocular (equalling a magni- 
fying-power of 750 diameters) utterly failed to discover the 
least trace of anything else which might correspond to the so- 
called vestibular bristle ; and it was therefore fully determined 
upon that there is no such body existing in the vestibule of the 
Epistylis. ‘The same observations were also made upon another 
species of Epistylis (2. grandis, Ehr.?), and upon Carchesium 
(C. polypinum, Ehr.) and Vorticella (V. nebulifera, Ehr.), with 
the same result. 
Notwithstanding this forewarning, it was very difficult to 
dispel the illusion when the vestibular cilia of Trzchodina were 
under investigation. If one observes attentively, however, it 
will be noticed, in the first place, that what appears to be a single 
cilium or bristle never projects beyond the tips of the cilia, 
which lie outside of the aperture of the vestibule ; and secondly, 
that when the tips of these cilia are followed along with the eye 
the row appears to terminate abruptly, and exactly at that point 
there seems to be the end of a bristle; 7. e. the tip of the latter 
ends just where the line of ciliary points terminates ; the two are 
coincident! Sometimes the point of coincidence is seen oppo- 
site the left side of the vestibular aperture, at other times oppo- 
site the middle of the same, or considerably to the right of it. 
Again, this point of coincidence appears to run rapidly from 
left to right, and then back again from right to left, as if the 
