EXPLANATION OF PLATE VII. 



FIG. 



1. HALISARCA LOBULARIS, Duj., a spiculc-less sponge, in vertical section, after 



F. E. Schulze, x 75. a/, apertures of afferent canals or pores leading to the 

 spheroidal monad-lined chambers or ampullaceous sacs, amp.\ ef, debouch- 

 ment 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., 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. cyt., superficial 

 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, 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 containing respectively 

 one and two ciliated swarm-gemmules; </, 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; /, in- 

 ternally projecting triradiate spicula ; g, swarm-gemmule in its earlier amoeboid 

 and non-segmented phase of development. 



