2* Notes on Eydatina 8enta. \^ioixn^if^iTS} 
a short lime they will swim straight on as vigorously as ever ; hut 
they soon hegin to slacken their pace, the characteristic cyhnder 
can scarcely traverse the hody, and after a few spiral contortions 
they lie motionless in the shapeless attitudes which Leydig has 
drawn in his four upper figures. 
On one occasion two of the parasites so expelled started together 
to cross the field of view, which they did in excellent style, never 
swerving from a straight line, and passing out of the field, as they 
entered it, neck and neck. I timed the race, and found that they 
swam through one-tenth of an inch, or about thirty times their own 
length, in a minute. 
Fig. 6 represents the animal flattened by the compressorium. 
There is a red spot (a) near the anterior portion of the body, and 
clear transparent spaces (h, h) which frequently change their posi- 
tion and form, though usually circular. The bodies (c, c, c) are of 
all sizes, from ^uVcrth of an inch downwards. They are hollow and 
brittle, and can be broken as at {d) by flattening the animal. Fig. 7 
shows one more highly magnified ; it is a roughly spheroidal globe 
with a half-projecting ring forming what may be termed its equator, 
and there are at the poles two funnel-shaped cavities whose narrow 
extremities are turned towards the centre and each other. As these 
bodies are thrown backwards and forwards by the animal, they turn 
over and move freely among each other. 
It is a difficult matter to make out satisfactorily the arrange- 
ment of the ciHa on Hydatina's head, owing to its incessant motion. 
I have repeatedly watched this rotifer while alive, by dark-ground 
illumination, as well as by transmitted light, and (availing myself 
of Leydig's method of killing it) have succeeded in obtaining fre- 
quent front, back, and side views of the extended cilia after the 
animal was dead ; and I do not think that either Cohn's or Leydig's 
figure fairly represents the trochal wreaths. That there are two 
continuous wreaths, one on the outer and the other on the inner 
edge of the disc, is obvious enough ; and those of the outer row are 
curved outwards, while those of the inner are curved inwards 
towards the buccal funnel ; but it is the middle row of much larger 
and straighter cilia which is perplexing. Cohn makes it a suc- 
cession of detached groups of straight cilia arranged hke fans on 
round protuberances between the inner and outer row. Leydig 
has, on the whole, a much more accurate figure of the trochal disc, 
but represents the middle row as " forming a continuous series." Now 
it does not appear to me that the middle row is either continuous 
or all broken up into tufts. It is with considerable diffidence that 
I question Cohn's or Leydig's statements ; but as these excellent 
observers do not agree, there seems to be room for a third opinion. 
There are, I think, three main groups of radiating cilia — one 
(Fig. 8, a) on a papilla placed towards the dorsal surface and in the 
