1921] NATURAL SCIENCES OF PHILADELPHIA. 109 



retractile pedicle of a Vorticella. Its whole appearance is that of 

 a very thin, thread-Uke secretion, where no structure is to be found; 

 and indeed, facts may be cited which go against the retractile ex- 

 planation : 



Looking at a fixed Pieridomonas for a sufficient time, a moment 

 at last comes when the pedicle suddenly loses its hold, the crown 

 of pseudopodia retracts, and the little animal swims rapidly away, 

 while the detached posterior thread or pedicle trails behind. In 

 such a state of rapid locomotion, with pedicle trailing or sometimes 

 with no pedicle at all (owning to its having been ruptured or having 

 collapsed), when coming into contact with some Infusorian or any 

 other obstacle in its way, the animalcule may suddenly jerk back- 

 ward, just as it did when attached. 



Under these conditions it seems hardly possible that the stalk 

 might be the cause of the sudden jerk; and we must look for another 

 explanation. 



The most evident distinctive character between Pter. scherffeli 

 and Pter. pidex is the possession, by the first of these species, of 

 lateral filiform appendages, which are wanting in the second. Lem- 

 mermami speaks of ^ these appendages as follows: "Besides the 

 anterior crown of pseudopodia, lateral radiating pseudopodia are 

 found." Neither Scherffel nor Lemmermann speak of these ''pseu- 

 dopodia" as being regularly distributed, and the first of these ob- 

 servers speaks of both anterior crown and lateral appendages in 

 the following terms: "The fine setose cilia, which radiate mostly 

 from the anterior part of the body, around the flagellum, but some- 

 times also start, in a smaller number, from the sides of the body, are 

 true pseudopodia." Both these authors, in fact, seem to consider 

 these lateral appendages as identical with those of the anterior 

 crown, and at the same time as irregularly located on the sides 

 of the body. But the reality is, that these particular threads, six 

 in number (or perhaps eight ?), are inserted in a single equatorial 

 Hne, or girdle, w^hich itself is, in most of the individuals, indicated 

 by a slight groove that divides the body into two parts, superior 

 and inferior. These threads are extraordinarily thin, are straight 

 and rigid, and are twice or even three times as long as the body; 

 they never are converted into flagella, and never retract into sep- 

 arate pearls, and are in no way comparable to the constituent 

 parts of the anterior crown — they rather seem to be identical with 

 those setae with which some Infusoria {e, g., Mesodinium pulex) 

 are provided. Now in these Infusoria the setae always work as a 



