THE ROTIFERA OF THE SCOTTISH LOCHS. 167 



Bdelloida. 



Structure. — The details of structure given in a previous paper (39) may be here 

 supplemented from later observations. 



Rostral processes. — The rostrum of Bdelloids bears generally, and perhaps 

 invariably, at least four different kinds of processes — the lamellae, the brush of cilia, 

 straight setae radiating from the tip close under the lamellse, and some thicker tactile 

 setae which arise singly or in pairs from about the centre of the base of each lamella. 



Most authors only mention the lamellse and cilia, without discriminating the various 

 kinds of cilia or setse. Janson (24) states that towards the ventral side the cilia are 

 elongated into ' Tastcilien ' ; Bryce (7) distinguishes between tactile and motile cilia, 

 without entering into details ; Weber (52) only mentions the tuft of cilia, but he figures 

 in Rotifer vulgaris two kinds of cilia — at each side a pencil of much longer cilia which 

 probably correspond to the tactile setae. Zacharias most clearly discriminates (55) the 

 crown or tuft of cilia and the two long ' Tasthaare.' The straight radiating setae I do 

 not find anywhere distinctly referred to. Most figures only show one kind of cilia, 

 which may be the tuft or brush, but in many cases probably indicate the radiating setae. 



Rostral lamellae. — There is a consensus of opinion among authors, including such 

 excellent observers as Zei.inka, Janson, Weber, and Bryce, that the rostral lamellse are 

 two distinct plates, which in those species where they appear to form a single two-lobed 

 hood are really overlapping at the bases. In deference to these authorities I refer to 

 them as lamellse, although in many cases they seem to me to form a single organ. In 

 microscopical matters it is especially necessary to avoid the bias of authority, and to 

 describe things as they appear to us, as Zacharias pleads (55) when giving an unorthodox 

 interpretation of the vibratile tags. I have never detected this overlapping of the 

 lamellse. In many species — Callidina russeola, C. teiraodon, and C plicata for common 

 examples — the lamellse appear quite distinct and far apart. In most species studied by 

 me they seem to form a single, more or less distinctly two-lobed hood. The meeting-point 

 of the two lobes generally forms a prominent beak, pointing forwards. In the viviparous 

 Philodinadse (P. macrostyla, etc., and the genus Rotifer), the appearance gives some 

 support to a suggestion made by Mr Bryce in a letter, that they are adnate (see 

 Plate V. fig. 21). 



In a great many instances, when the lamellse are most fully extended, the two-lobed 

 character disappears, and the organ appears as a simple hood, like that of Metopiclia, 

 Stephanops, or Diglena, merely curved forward at the tip (Plate II. fig. 8^). 



The brush, or tuft or crown of cilia. — Most conspicuous of the rostral cilia is 

 usually the tuft. These cover most of the surface of the evertile tip, and are usually 

 gathered together into a compact brush, which possesses an automatic motion similar 

 to that of the wreaths, but less regular as to direction. By means of them many species 

 can glide forward rapidly, thus supplementing the Bdelloid step. They probably also 

 assist the wreaths, as they are often in active motion when the animal is feeding, 

 TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 7). 23 



