26 Mr. H. J. Carter on the Ultimate Structure o/Spongilla. 



Independently of all these structures, together with an innu- 

 merable number of minute contracting vesicles, the investing 

 membrane is so transparent, that every part of its cavity can be 

 seen as clearly as if there were no membrane at all. 



Parenchyma. — This consists of a mass of gelatinous sub- 

 stance (PL I. fig. 1 c, c), in which are imbedded the smooth spi- 

 cules and ovi-bearing cells, and through which pass the afferent 

 and efferent canals. 



Ovi-bearing cells. — The ovi-bearing cells do not burst and 

 allow their contents to become indiscriminately scattered through 

 the gelatinous mass in which they are imbedded, but each be- 

 comes developed separately and entire in the following way, viz. 

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

 granular mass by the former losing their defined shape and 

 passing into small monociliated and uuciliated sponge-cells; 

 this mass then becomes spread over the interior 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 undu- 

 lating 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 am- 

 pullaceous, spherical sac. The cilia may be now seen undulating 

 in the interior; and if the Spongilla is fed with carmine, this 

 colouring matter will not only be observed to be entirely con- 

 fined to the ampullaceous sacs, but when the Spongilla is torn 

 to pieces and placed under a microscope, particles of the car- 

 mine will be found in the interior of the monociliated as well 

 as in that of the unciliated sponge- cells (figs. 2, 3, 4, 5) ; 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. 



Sometimes an isolated ovi-bearing sponge-cell which has 

 escaped from the general mass, may be seen to have undergone 

 the same development by itself in the watch-glass ; but in this 

 case there appears to be no aperture, for particles of carmine 

 brought into contact with it indicate no currents about its ex- 

 terior, while, within, the cilia may be undulating as actively and 

 as evidently as if it were in situ. Another proof also of the 

 absence of an aperture is, that under this condition the ampul- 

 laceous sac encloses the particles of carmine which are in contact 

 with its exterior, after the manner of Amoeba. 



England, and mentioned the fact at the British Association (Athenseum, 

 oOth August, 1856). His paper in the Quart. Journ. Microscop. Science 

 I have not vet seen. 



