118 PROCEEDINGS OF THE ACADEMY OF [PaRT I 



the University. Most generally it was attached to the threads of 

 a small Nostoc, either solitary or with one or two companions, but 

 never in big colonies. 



The Httle capsule (Plate V, fig. 9), very thin and colorless, is 8[x 

 in length; ovoid or somewhat fusiform in shape, pointed behind and 

 opened anteriorly in a large aperture, at right angle to the longi- 

 tudinal axis. This opening, however, is rather variable in breadth, 

 according not only to the individuals, but also to the orientation 

 of the animal; the capsule, in fact, is a little compressed, more so 

 at the opening than anywhere else, and at the same time proves 

 somewhat elastic; when the animalcule protrudes for half its length 

 out of the shell, it presses against the sides and makes the opening 

 rounder, and when suddenly retracting the edges of the aperture 

 contract. The capsule is affixed to the substratum by means of 

 a very thin pedicle, a simple colorless filament, whose length is 

 exceedingly variable, and is commonly twice or three times as great 

 as that of the capsule, sometimes even more. Frequently it is 

 seen to terminate at the point of fixation in a small bluish knob 

 or cushion, and from the fact that the volume of the knob is in 

 inverse proportion to the length of the pedicle, one can infer that 

 it furnishes the material for the lengthening of this thread. This 

 growth of the pedicle, however, must be very quick, and reaches its limit 

 a very few moments after the fixation of the animalcule; such is, at 

 any rate, the inference that might be drawn from the fact that speci- 

 mens with very short stalks (Plate V, figs. 9, 12), kept under ob- 

 servation for ten, twelve and twenty-four hours, never showed 

 during that time any lengthening of their stems. Very likely the 

 length of the pedicle is in some relation with the conditions of the 

 medium; for instance, in some material which had been kept a long 

 time since it was collected, I once found all the individuals short- 

 stalked (Plate V, fig. 12). The animalcule hardly fills half of the 

 capsule. In its perfectly expanded state, it is pear-shaped. At the 

 anterior extremity and on one side is seen projecting a protoplasmic 

 appendage which looks at first sight like a very short pseudopodium ; 

 but in reality the ectoplasmic layer developed here in a collar-like 

 expansion, hardly conspicuous on one side but very extended on 

 the other, and whose function is to hold fast the small particles of 

 food that the flagellum has thrown down. The flagellum, which 

 starts from the anterior depression, is strong and very distinct, 

 and of very remarkable length, attaining five or even six times the 

 length of the body. When the animalcule is quietly fishing, with 

 its body half protruded from the shell (Plate V, fig. 9) , the flagellum 

 is seen pointing directly upwards, and hardly seems to move, but 

 sometimes is only distinguishable up to the half of its length, the 

 tip only vibrating. The animalcule does not, as a rule, remain 

 very long in the extended state; it suddenly retracts inside the shell 

 and becomes ovoid in shape, but for a very short time only, soon ex- 

 panding again. The behavior of the flagellum is then very inter- 

 esting to follow: when the animalcule retracts, the flagellum coils 



