1921] NATURAL SCIENCES OF PHILADELPHIA 119 



in a perfectly regular manner, so as to simulate a coil of rope with 

 four or five turns, which stands upright over the retracted body (Plate 

 V, fig. 11); then as soon as the animalcule begins expanding (Plate V, 

 fig. 12), the coils rapidly unroll and are flung far out like a lasso 

 thrown by an invisible arm. The retraction of the body down to 

 the bottom of the cell is effected by means of a thread, which is 

 seen affixed to the very tip of the inside wall, and looks — but only 

 looks — like a continuation of the pedicle inside the envelope; from 

 this basal point the thread passes up along the body and comes to 

 an upper fixation quite near the base of the anterior flagellum ; in 

 fact, this posterior thread is nothing but a flagellum, which has 

 temporarily lost its normal functions to acquire those of a retractile 

 organ. The nucleus is spherical, and situated posteriorly, near 

 one side of the body; it is rather pale, not very distinct, and shows 

 a large central caryosome. The contractile vesicle is at the pos- 

 terior extremity, behind the nucleus; sometimes a second one is 

 to be seen, but though being able to empty and fill again from time 

 to time like an ordinary contractile vesicle, it can hardly be con- 

 sidered as such, but is rather an accessory vacuole, whose function 

 is to refill the true vesicle when empty. 



I was not able to study the division inside the envelope, but on 

 the 16th and 17th of February, I found, among a great number of 

 empty cases, a good many small Flagellata which were rapidly 

 swimming about, and whose appearance was that of individuals 

 belonging to this species after leaving their shell; all characteristics 

 were the same, except for the form of the body, that of a true, naked 

 Flagellate, with two flagella, one of which was traihng behind (Plate 

 V, fig. 13) ; it was certainly the retractile thread, which in this new 

 flagellated state had recovered its true nature. It would have 

 been interesting to notice the fixation of these small Flagellates 

 and the construction of the shell, but my attempts in that direc- 

 tion were not successful. 



The rather numerous species which make up the genus Bicoeca 

 are all of very small size, and the distinctive characters are some- 

 times very hard to recognize; the form of the capsule, however, is 

 very constant, and the length of the fiagellum, and the position 

 and number of the contractile vesicles, also furnish important facts. 

 The taxonomy of the genus is however, anything but clear. Bicoeca 

 and the construction of the shell, but my attempts in that direc- 

 lacustris J. Clark, for instance, as indicated by Lemmermann (27), 

 is considerably different from the same species as figured and 

 described by S. Kent (this latter observer speaks also of a second 

 very small anterior flagellum, which character would refer to 

 Stokesiella) , and at the same time both forms are not very far from 



