EXPLANATION OF PLATE VIL 

 Fig, 



1. Halisarca lobularis, Duj., vol. i. p. 169, a spicule-less sponge, in vertical 



section, after F. E. Schulze, x 75. — af, apertures of afferent canals or pores 

 leading to the spheroidal monad-lined chambers or ampullaceous sacs, a7np ; 

 ef, debouchment of efferent canal conducting from the ampullaceous sacs 

 to the deeper interstitial canal-systems, which finally open upon the larger 

 excurrent orifices or oscula ; a, b, c, d, e,f, progressive phases of development 

 by segmentation of swarm-gemmules in the deeper substance of the sponge, 

 these occupying the positions previously filled by the ampullaceous sacs, and 

 from which, by metamorphosis, they are obviously derived ; g, younger and 

 more rudimentary phase of these bodies, embedded in the cytoblastema 

 adjacent to the ampullaceous sacs. 



2. ESPERIA sp., vol. i. p. 169, a siliceous-spiculed sponge, in vertical section, showing 



grape-like arrangement of the ampullaceous sacs round a single afferent or 

 pore system, x 500. — af, entrance of afferent canal or pore, the arrows 

 denoting the course followed by the incurrent stream of water ; s. cyi, super- 

 ficial cytoblastematous layer, bounding the sponge-periphery and extended 

 canopy-wise over the distal extremities of the spicula ; sp, acerate spicula ; 

 amp, ampullaceous sacs ; c, amoebiform cytoblasts ; a b, imperfectly deve- 

 loped ampullaceous sacs in the deeper substance of the cytoblastema ; 

 2 a, minute bihamate spicula from the structureless cytoblastema, x 800. 



3, 4. Grantia compressa, Bowerbank, vol. i. p. 169, a calcareous-spiculed sponge. — 

 3, Segment of an entire transverse section, x 300, showing at a central 

 cavity or cloaca receiving currents passed through the surrounding ciliated 

 or monad-lined chambers, b,b ; c, c, two such monad-lined chambers con- 

 taining respectively one and two ciliated swarm-gemmules ; d, external 

 fringe of recurvate-clavate defensive spicula. 4, One entire, and a portion of 

 a second monad-lined chamber, x 600 ; af, afferent canal or pore by which 

 currents are received from the external water ; ef, efferent canal conducting 

 to the central cloacal chamber ; m, collar-bearing monads ; d, external 

 defensive spicula ; i, internally projecting triradiate spicula ; g, swarm- 

 gemmule in its earlier amoeboid and non-segmented phase of development. 



