108 PROCEEDINGS OF THE ACADEMY OF [PaRT I 



only one possible, and much more frequently the small food particle, 

 without coming into contact with the extended threads, directly 

 gets to the surface of the body, where a big vacuole is immediately 

 formed around it; but it remains certain that these rigid filaments, 

 twice or three times as long as the body, form together some- 

 thing like a net, and as such are of very evident importance. But 

 besides these functions as prehensile organs, such as are observed 

 in the pseudopodial state, could not we imagine functions of a differ- 

 ent nature, due to the flagelliform state of these particular threads? 

 When describing for the first time, in 1890, the genus Pteridomonas, 

 I felt confident I had seen the small pearls at the base of the central 

 flagellum suddenly unroll and fling the little animal backward; 

 the flagellopodia, in fact, were to be compared to the frond of a 

 fern and not to a compact shapeless body. But Scherffel, in 1901, 

 proposed another explanation; — he looks upon the threads as true 

 pseudopodia, quite incapable of passing into another condition; the 

 two smaller flagella, which are at times seen left and right of the 

 central flagellum, "are in no way two pseudopodia which have 

 taken to an undulating condition, as Penard thinks. Their func- 

 tion is unknown"; and a little further on he adds: "The jumps are 

 due to the energetic and sudden contractions of the fixed stalk." 

 Much later, in 1904, after observing some specimens of Pterido- 

 monas from the Lake of Geneva, I had myself abandoned my former 

 explanation to adopt the Scherffel theory, and today, after a much 

 more thorough examination, I feel confident the rolling and unroll- 

 ing explanation was a mistake; but is the sudden jerk backward 

 due really to a contraction of the pedicle? 



In Pteridomonas, the body is protracted behind into a thread, of 

 extraordinary thinness, like the thread of a spider; and this 

 thread or pedicle, four, six, or as much as eight times as long as 

 the body, firmly holds the animalcule to the substratum. In 

 such an attached condition, the little organism is generally seen 

 fishing, with its central flagellum actively swinging, and the threads 

 of the anterior crown rigid, unmoved, and expanded at their full 

 length, but from time to time the animalcule suddenly disappears 

 from sight, and rapidly comes back, a jerk has thrown him to one side 

 but the fixed pedicle prevented any definitive removal. This pos- 

 terior thread is thus very important in enabling, for instance, the 

 animalcule to escape the contact of an enemy and yet remain in 

 the same region; but it is hardly to be expected that the pedicle 

 might do more than attach the body, and be comparable to the 



