THE ROTIFERA OF THE SCOTTISH LOCHS. 169 
A peculiar papilla has been seen as yet only in two species, Philodina laticeps 
and Callidina magna (fig. 6). It is a large, elevated, gently tapering, conical peg, 
truncate or slightly expanded at the tip, and bearing there a number of very short 
motile cilia. 
Perforated spurs.—lt has been asserted by various authors (ZELINKA, JANSON, etc.) 
that the spurs of certain species (Callidina russeola, C. vorax, C. parasitica, etc.) are 
perforate at the tips, and that ducts convey mucus from the foot-glands to these pores. 
I have never been able to satisfy myself that any species which I have studied had 
habitually mucus ducts to the perforate spurs. In two instances, however, have I seen 
mucus exuding from the tips of the spurs. One example of Callidina scarlatina and 
one of Philodina acuticornis (figs. 5, 9d) had the mucus forming a thick deposit round 
the tip of each spur, and gradually tapering to a drawn-out thread, which made the 
spurs appear longer than they really were. The deposit round the two spurs was too 
symmetrical to be attributed to accidental contact with the mucus of the toes. 
MIcRODINADA. 
Systematic position.—The relation of the various families of Rotifera to one another 
is very puzzling. One group of characters would lead us to associate certain families ; 
other groups would lead to different combinations. The discovery of aberrant animals 
generally assists in the elucidation of attinities, though they often destroy the symmetry 
of our classifications. Does Microdina help us to understand the affinities of the 
Bdelloids ? 
The jaws, which I suggested (39) were a kind of link between the Bdelloida and the 
Melicertadz, really lead almost as directly to many families of Ploima, and even to the 
Scirtopoda. 
The Microdinade and Seisonidee may be profitably compared. Both are true 
Digonata, though this is not brought out in my original figures of Microdina (39). 
The relationship of the Bdelloids and Seisonidze is perhaps best shown in Lunnp’s classi- 
fication (31), where he makes them orders of Digonata; but Microdina somewhat 
diminishes the distance between them. Sezson approaches the Bdelloids not only in 
the Digonate character, but in the telescopic neck and foot, while the two tufts of sete 
recall the wheels of the Bdelloid corona. Microdina approaches the Seisonidze in the 
shortened gullet, reduced corona (Paraseison), and jaws departing from the ramate 
type. Sezson has jaws quite remote from the ramate, and more resembling some of the 
Notommatade, and most conspicuously differs from Microdima in the union of gullet 
and cesophacus. 
Sezson is highly specialised, in adaptation to a peculiar situation and mode of life. 
Microdina does not occupy a peculiar situation; it leads a free life, in company with 
many other Bdelloids, on mosses and other aquatic plants. It merely gets its living in 
another manner, and is modified accordingly. The lack of discs and the very strong 
