FLAGELLATE INFUSORIA AND ALLIED ORGANISMS. 71 



in individuals, are thicker and longer (fig. T a) ; at their 

 attached base a flattened portion serving for attachment is 

 seen under favorable circumstances, whilst the stem itself 

 appears tubular, dark sides, and a clear homogeneous axis 

 substance being distinguishable. Occasionally the usually- 

 colourless stem is tinged of a somewhat yellowish brown. 



The individuals forming the colony spring from the upper 

 end of the stem, each being carried upon a delicate proto- 

 plasmic stalk, which passes directly into the hinder end of 

 the organism. These stem-like prolongations of the hinder 

 poles are not contractile, at least not in any noticeable 

 degree. The flagellum springs from the centre of the obtuse 

 anterior pole of the body. When it is at rest it frequently 

 falls, somewhat curled in a very characteristic way. The 

 delicate membrane-like collar surrounds the blunted anterior 

 pole (fig. 7 a — c) ; it is usually seen in optical section as 

 two dark diverging lines, which at first give the impression 

 of two accessory flagella, and for these they have been 

 occasionally mistaken. 



Fresenius described the collar as a delicate, blunted ap- 

 pendage, from which a cilium causing motion (Bewegungs- 

 faden) projected. 



The size and appearance of the collar are exceedingly 

 variable ; sometimes it projects only very slightly beyond 

 the anterior end. Separate specimens have been seen 

 swimming freely, which did not possess any trace of a collar. 

 Generally it is of considerable height, as in fig. 7 a, b, oc- 

 casionally (fig. 7 c) it is a very noticeable object. Clark has 

 observed that this change in the height of the collar is very 

 rapidly executed in one and the same individual, that the 

 funnel can be drawn in, that is, can be made to blend with 

 the protoplasm of the body, and can be again protruded. 

 This fact, in connection with its conduct during fission, 

 points to the conclusion that the collar is only the protoplasm 

 of the anterior end of the body modified in a peculiar way, 

 and that it may be regarded in a certain sense as a further 

 modification of the lip-like prolongation of such an organism 

 as Bicosoeca. 



The collar cannot alter its shape without at the same 

 time changing its height. Whilst the organism is in move- 

 ment it is able to contract, and the shape becomes more 

 rounded, whilst the free edge of the collar is so much con- 

 tracted that it almost closes (fig. 7 d), although its usual 

 condition is that of a more or less funnel-shaped opening. 

 According to Clark, the cytostome or spot where the in- 

 gestion of food takes place, is at the anterior end of the 



