394 



THE MICROSCOPE. 



tents to become indiscriminately scattered through the 

 gelatinous mass in which they are imbedded, but each 

 becomes developed separately in the following way : — the 

 ovules and granules of the ovi-bearing cells subside into a 

 granular mass by the former losing their defined shape 

 and passing into small mono-ciliated and unciliated sponge 

 cells ; this mass then becomes spread over the intei'ior 

 surface of the ovi-bearing cell, leaving a cavity in the 

 centre, into which the cilia of the monociliated sponge- 

 cells dip and keep up an undulating motion ; meanwhile, 

 an aperture becomes developed in one part of the cell 

 which communicates with the adjoining afferent canal, and 

 thus the ovi-bearing cell passes into an ampullaceous 

 spherical sac. The cilia may now be seen undulating in 

 the interior ; and if the Spongilla be fed with carmine, this 

 colouring matter will not oidy be observed to be entirely 

 confined to the ampullaceous sacs, but when the Spongilla 

 is torn to pieces and placed under a microscope, particles 

 of the carmine will be found in the interior of the mono- 

 ciliated and unciliated sponge cells, proving that of such 

 cells the ampullaceous sac is partly composed. This sac 

 then must be regarded as the animal of Spongilla, as 

 much as the Polype- cell is regarded as the animal of the 

 Polype, and the whole mass of Spongilla as analogous to 

 a Polypidom. 



" The united efforts of all the ciliated sponge-cells in 

 the ampullaceous sac are quite sufficient to produce a con- 

 siderable current, and thus catch the particles of food as 

 they pass through the afferent canals. Thus we find 

 Spongilla composed of a number of stomachal sacs im- 

 bedded in a gelatinous substance permeated with spicules 

 for its support, and an apparatus for bringing them food, as 

 well as one for conveying away the refuse, while the nourish- 

 ment abstracted by the process of digestion common to 

 Rhizopodous cells (e.g. Amoeba), no doubt passes thixmgh the 

 intercellular gelatinous substance into the general develop- 

 ment of the mass ; and if right in comparing the ampul- 

 laceous sacs to the stomachal cavities of the simplest 

 polypes, are we not further justified in drawing a resem- 

 blance between the ciliated sponge-cells and those which 

 line the stomach of Cordylophora, of Otostoma, and many 



