PROTOZOA AND SPONGES 431_ 



they have the closest affinity. Their only peculiarity is 

 their tendency to run out into long ribbons or attenuated 

 threads, which, however, coalesce and unite whenever they 

 come into mutual contact, and thus we see the threads 

 branching and anastomosing with the utmost irregularity, 

 usually with broad triangular films at the points of diver- 

 gence and union. 



There can be no doubt that the object of these length- 

 ened films, which are termed pseudopodia, is the capture 

 of prey or food of some kind; perhaps the more sluggish 

 forms of minute animalcules, or the simpler plants. These 

 the films of sarcode probably entangle, surround, and drag 

 into the chambers of the shell, digesting their softer parts 

 in temporary vacuoles, and then casting out the more solid 

 remains, just as the Amoeba does. 



Though this beautiful array was so very deliberately 

 put forth, it is, as you perceive, very rapidly withdrawn 

 on any disturbance to the animal, as when we agitate the 

 water, by slightly moving or turning the cover of the live- 

 box. Another fact, of which you may convince yourself 

 by watching manifest though small changes of position in 

 the shell while under observation, is, that it is by means 

 of the adhesion and contraction of the pseudopodia that 

 the animal drags itself along a fixed surface. This it can 

 effect so assiduously that I frequently find them in the 

 morning adhering to the tank-sides three or four inches 

 from the bottom, though on the previous evening none 

 were visible on the glass. Thus they must crawl, on 

 occasion, from a hundred to a hundred and fifty times 

 their own diameter in a night. 



The structure of a Sponge is much the same as that 

 of these animals, with the exception that its solid part or 



