AND TWELVE NEW SPECIES OF ROTIFERA OF THE ORDER BDELLOIDA. 369 
animals. They are distinguished by bulk of body, long and powerful foot, large strong 
spurs, and usually ample corona. The life agrees with them. Signs of degeneration 
are not lacking, however. Their affinities are with genera which normally possess eyes, 
but most of these parasites are blind, and have smaller brains than are possessed by free- 
living species of the same genera. 
Symbiosis.—A number of Bdelloids have the foot of a peculiar type, in which there 
are no distinct toes, their place being taken by a disc, which is perforated by numerous 
pores for the passage of the mucus. It has been suggested that the species having this 
kind of foot live in symbiotic relationship with certain Hepatics, such as Frullania, 
which have some of their leaves in the form of little pitchers. The suggestion is plaus- 
ible, inasmuch as such Hepatics are seldom found without the pitchers occupied by the 
Rotifers. There is, however, something to be said against the belief that the relation is 
one of symbiosis. There is no evidence of any advantage to the plants, though it has 
been guessed that the animals are in some way beneficial to them, and that to obtain 
this benefit the pitchers have been developed as an attraction to Rotifers. It is more 
probable that the pitchers of the Hepatics serve the sole purpose of retaining moisture, 
and that many species of Rotifers have found and taken advantage of those little 
reservoirs. In that case there is no symbiosis, only a mild form of parasitism. Bdelloids 
| having the discoid foot are not only found on Hepatics. They abound in many other 
situations. Nor are they the only Bdelloids which frequent Frullania cups. Many 
species with the ordinary foot are commonly found there. It might be supposed that a 
Bdelloid would have less need of a strongly adhesive foot in the shelter of a Frullama 
pitcher than in many more exposed situations. The discoid foot is an advantage to a 
species in any situation, and it is to be noted that all the species having it are large, 
powerful animals. 
Two species having the discoid foot are here described. One is from a lake, the 
other from a pond, and neither has yet been found on Hepatics. 
Formation of food-pellets.—Four of the species described in this paper belong to 
that section of the genus Callidina in which the food is moulded in the cesophagus into 
pellets. All the animals having this characteristic agree in many other points of 
structure, such as the small size of the corona, and form a very natural group. Most of 
them have the neck very long and the gullet correspondingly elongated, and forming a 
large loop when the neck is contracted. The pellets differ greatly in consistence in 
different species. Some are loosely put together, and quickly disintegrate when passed 
into the stomach. In some species they seem to be mixed, while in the cesophagus, with 
something which gives them coherence. Such pellets maintain their size and form 
unchanged during the whole of their passage through the alimentary canal, and are 
finally voided entire. When first passed into the stomach they are granular, and often 
dark from the admixture of food particles. They gradually lose the granular character 
as they move through the stomach, till when passed out they are clear spheres. 
