V] OF COLLARED CELLS 429 



When the cell dies, that is to say when motion ceases, the collar 

 immediately shrivels away and disappears. It is notable, by the 

 way, that the edge of this little mobile cup is always smooth, never 

 notched or lobed as in the cases we have discussed 

 on p. 390 : this latter condition being the outcome 

 of a definite instability, marking the close of a 

 period of equihbrium. But the vibratile collar of 

 Codosiga is in "a steady state," its equihbrium, 

 such as it is, being constantly renewed and per- 

 petuated, like that of a juggler^s pole, by the 

 motions of the system. Somehow its existence is 

 due to the current motions and to the traction 

 exerted upon it through the friction of the stream 

 which is constantly passing by. In short, I think 

 that it is formed very much in the same way as 

 the cup-hke ring of streaming ribbons, which we 

 see fluttering and vibrating in the air-current of „. ,,^ 



a ventiktmg fan. If we turn once more to 

 Mr Worthington's Study of Splashes, we may find a curious 

 suggestion of analogy in the beautiful craters encirchng a central 

 jet (as the collar of Codosiga encircles the flagellum), which we see 

 produced in the later stages of the splash of a pebble. 



Another exceptional form of cell, and beautiful manifestation of 

 capillarity, occurs in Trypanosomes, those tiny parasites of the 

 blood which are associated with sleeping-sickness and certain other 

 dire maladies of beast and man. These minute organisms consist 

 of elongated sohtary cells down one side of which runs a very 

 delicate frill, or "undulating membrane," the free edge of which is 

 seen to be sHghtly thickened, and the whole of which undergoes 

 rhythmical and beautiful wavy movements. When certain Trypano- 

 somes are artificially cultivated (for instance T. rotatorium, from the 

 blood of the frog), phases of growth are witnessed in which the 

 organism has no undulating membrane, but possesses a long cihum 

 or "flagellum," springing from near the front end, and exceeding 

 the whole body in length*. Again, in T. lewisii, when it reproduces 

 by "multiple fission," the products of this division are Hkewise 



* Cf. Doflein, Lehrbuch der Protozoenkunde, 1911, p. 422. 



