*joSi. ji^iTff T -^^^^^ Eydatina Senta. 23 
filled from it, there were plenty of Hydatina, and this small 
reservoir continued to supply me with fresh specimens for nearly 
a fortnight, while they were never to be found in the puddle. At 
the end of the fortnight all the rotifers disappeared, although, so far 
as I could see, there was no change of any of the circumstances 
under which they had previously thriven. The only thing which 
had altered was the temperature, which had suddenly fallen, and 
perhaps this was a fatal change to rotifers in so small a quantity of 
water as that contained in a hoof-print ; but why they should have 
originally deserted the puddle for such a preposterous residence I 
cannot imagine. 
Almost all the specimens I obtained from Bedminster contained 
internal parasites ; while a few had what appeared to be the mycelium 
of a fungus growing in the space between the cuticle and the internal 
organs. The white network of the mycelium stretched into every 
portion of this space, and surrounded (though loosely) the stomach, 
mastax, ovary, &c. &c. ; frequently crossing the larger muscles and 
bending them out of their proper directions ; but the creature did 
not seem to be distressed in any way by this parasitic growth, and 
its motions were quite as active as those of a healthy Hydatina. 
Fig. 1 represents Hydatina held down by a compressorium, and 
shows the mycehum which I have drawn as accurately as the 
intricate nature of the meshes would permit; and at Fig. 2 is 
shown a small portion of the mycehum more highly magnified. 
I isolated one or two of the rotifers thus affected, in the hope 
of seeing a further development of the fungus ; but I was not suc- 
cessful, for they all soon died. 
The internal parasites of Hydatina I have often seen. They 
were figured first by Leydig ; and a translation of his paper, in 
which there is a notice of them, was given in the ' Annals of Natural 
History ' for 1857. They are of a narrow oval form, and average 
^Jo th of an inch in length ; and when in Hydatina's stomach are 
in incessant and vigorous motion, jerking the contents of their bodies 
forwards and backwards, so as to make a cylindrical mass travel 
rapidly to and fro in the most curious manner. 
Figs. 3, 4, and 5 are different views of the same animal when 
in unrestrained motion. While passing through these various 
shapes, it pushes its way quickly up and down Hydatina's stomach, 
usually taking up its position close to the upper extremity, and a 
little to the side of the opening into the oesophagus. Even when 
the anterior portion of the parasite is right against the walls of the 
stomach, the cylindrical wave never ceases to travel up and down 
its body, and occasionally the motion is complicated by a spiral 
movement being added to the other. 
It not unfrequently happens that when the parasites in their 
travels reach the lower stomach they are suddenly expelled, and for 
