THE ROTIFER A 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. — It 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 

 svmmetrical to be attributed to accidental contact with the mucus of the toes. 



MlCRODINADiE. 



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 affinities, 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 

 Melicertadae, really lead almost as directly to many families of Ploima, and even to the 

 Scirtopoda. 



The Microdinadse and Seisonidse 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 Seisonidse is perhaps best shown in Lund's classi- 

 fication (31), where he makes them orders of Digonata; but Microdina somewhat 

 diminishes the distance between them. Seison approaches the Bdelloids not only in 

 the Digonate character, but in the telescopic neck and foot, while the two tufts of setae 

 recall the wheels of the Bdelloid corona. Microdina approaches the Seisonidse in the 

 shortened gullet, reduced corona (Paraseison) , and jaws departing from the ramate 

 type. Seison has jaws quite remote from the ramate, and more resembling some of the 

 Notommatadse, and most conspicuously differs from Microdina in the union of gullet 

 and oesophagus. 



Seison 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 



