SPONGE WEAVERS. 121 



organs of the sponge, and occasionally we find minute 

 creatures permanently located in its large cavities, with- 

 out appearing to cause it the slightest inconvenience." 



At certain periods of the year portions of this 

 sarcode, detached from the living animal, are capable 

 of a certain amount of locomotion. It resembles, 

 perhaps most nearly, the slow, gradual movements of 

 that curious little creature, the Amoeba, and consists in 

 a constant change of form, with progress in different 

 directions. Several independent observers have 

 described these movements, and most of them have 

 found them to occur at certain periods, and not at 

 others, whatever the reason may be. 



The living animal, or the units which go to make 

 up the living animal of the sponge, has of late years 

 been the subject of controversy, and there are still, 

 perhaps, two principal opposed views, one in favour 

 of an analogy with the polypes, and the other with 

 flagellate monads. The latter view is now altogether 

 the most general. " The true essential part of a 

 sponge," writes one who adheres to the latter view, 1 

 " is composed of structureless sarcode, and nucleated 

 cells, placed side by side, with a flagellum, some cells 

 having a hyaline collar protecting the flagellum. 

 These latter cells line all the passages leading from 



1 "On the Natural History and Histology of Sponges," by 

 B. W. Priest, in Quekett Microscopical Journal, vol. vi. p. 232. 

 1881. 



