THE ROTIFERA OF THE SCOTTISH LOCHS. 171 



Philodina. — Toes four. There may or may not be eye-spots ; when present, they 

 are cervical. The genus is divided into three sections, denoted by the letters A, B, C. 

 The first two are only for convenience ; the third is natural (except P. laticornis), and 

 should perhaps form a separate genus. 



A. Oviparous, eyes cervical. 



B. Oviparous, eyes absent. 



C. Viviparous, eyes present or absent. 



P. brevipes, Murray. (Plate I. figs. 2a to 2c.) 



Though occasionally locally abundant, the species is uncertain in its occurrence. 

 Its abundance in Loch Morar in 1903-4 enabled me to study it more fully than when 

 the animal was first described (39), and better drawings were obtained, which are here 

 reproduced. 



The straight setae on the rostrum are of extraordinary length, projecting at each side 

 considerably beyond the sides of the head. There are thick tactile setse under each lamella 

 (fig. 2b) ; it is uncertain whether there is a pair at each side, as there is in P. macrostyla. 



Seven pairs of vibratile tags were seen — at each side two in the head, on each branch 

 of the forked canal, one pair in the first cervical segment, and four pairs in the central 

 segments. They are set at equal distances) apart, but there is a gap in the series, or a 

 wider interval, at the level of the mastax, or between the third and fourth tag at each 

 side, counting from the front. This hiatus appeared in several individuals studied, so 

 I hardly think the tags (which are conspicuous) have been overlooked. 



The foot is three-jointed, but there is often an appearance of four joints. In 

 fig. 2c I show how this is brought about. Each telescopic segment of the foot of 

 a Bdelloid consists of a somewhat firm cylinder. These are joined together by soft, 

 flexible skin, which renders the telescoping possible. Where the soft skin joins the 

 firmer cylinder there is often a little elevated ridge, more marked than usual in the 

 present species. In the fullest extension of the foot this soft skin, with its limiting 

 ridge, appears like an extra joint. 



In Loch Morar, in 1903, all the examples found had a hair-like growth on the head. 

 Mr Bryce considers this hair as fungoid, and attributes to such a growth the P. hirsuta 

 of various authors. It is difficult to understand the symmetry of the hair, and its 

 confinement to the head. In P. laticeps, similarly affected, the growth was confined 

 to the trunk. 



Differing from P. citrina in many points, careful study is necessary to discriminate 

 the two species. Less massive than P. citrina, P. brevipes is also of quick, restless 

 habits, very different from the elephantine deliberation of its relative. The marked 

 characters of rostrum and foot are often difficult to observe. The number of teeth is 

 not a safe character, as P. brevipes has the usual 2 4- i/i + 2, with the third tooth not 

 infrequently as thick as the others. 



