382 MR JAMES MURRAY ON A NEW FAMILY 
Habits.—Parasitic on insect larvee which live in running water. It has been found 
on larvee of several species, adhering to the thorax, between the bases of the legs. When 
separated from its host it is little disturbed, immediately begins to creep actively about, 
and readily feeds. When feeding it is very restless, and sweeps the great corona from 
side to side and all over the field. The apparent breadth of the corona is often in- 
creased by a peculiar habit the animal has of pulling in the sides of the trunk till it 
resembles a stem supporting a large flower. It is then more like one of the large- 
headed Rhizota, such as Cfeistes velatus, than a typical Philodine (fig. 11h). When 
feeding it draws the rostrum in till it is depressed below the surrounding surface of the 
head. 
Comparison of P. laticeps with P. laticornis.—The two species resemble one another 
very closely in some characters, and differ greatly in others. The agreement is so close 
that it is difficult to avoid the conclusion that they are related animals. On this 
supposition an interesting comparison of the differences of structure in relation to the 
different modes of life may be made. P. laticeps is a parasite; P. laticornis has only 
been found free. They agree in general form, in the rostrum, spurs, and long curved 
ventral toes, so closely that but for the longer foot of P. /aticeps the same drawing of 
the extended animal could represent both. P. laticornis has a large brain and eyes, 
smal] papillee on discs, larger antenna, and shorter three-jointed foot. P. laticeps has 
much larger corona, very large papille on the discs, shorter antenna, longer four-jointed 
foot, much smaller brain, and no eyes. If the parasite P. /aticeps has been derived from 
the free-living P. /aticornis, it is interesting to note that while it has gained a larger 
mouth, it has lost its eyes and most of its brain. Should P. laticornis, as is possible, 
prove to be also parasitic, the force of the comparison is diminished, but not altogether lost. 
The habit of swimming might enable a parasite to change its host when necessary, and 
so render it less dependent, and the retention of the large brain and eyes may be 
attributed to this habit. 
P. laticeps is oviparous, P. laticornis viviparous. This is the only instance known 
to me of closely related Bdelloids differing in the mode of reproduction. 
Habitat.—In a little stream entering Inchnacardoch Bay, Loch Ness. Very 
abundant during the winter of 1903-4. Any handful of Fontinalis taken from this 
stream and shaken in water yielded thousands of examples. Early in the summer of 
1904 the stream dried up, and remained in this condition till October. When the water 
returned to the channel insects and rotifers had disappeared, and up till the end of 
November neither had again been found. Similar streams in the same district were 
searched, but though larvee were found, there were no rotifers upon them. 
Philodina humerosa, n.sp. (Plate IV. figs. 4a to 4g.) 
Specific characters.—Small, dull grey, strongly plicate on trunk. Ventral trans- 
verse folds, fourteen or fifteen. Central sete on discs spring from large conical 
