Ampullaceous Sacs and Spongozoa. 437 



but that it is rendered almost equally so in the most prominent 

 parts by the pink colour of the spongozoa in the living con- 

 dition of the sponge. Hence we have thus a distinct organ 

 presented to us for consideration, viz. the ampullaceous sac. 



And first, as regards its form in H. lobular is, this is in-egu- 

 larly round, but, in many instances, distinctly conical elongate ; 

 for all these sacs are neatly defined, as before stated, by a 

 translucent linear interval, -which may thus be compared to the 

 crystalline calcspar that surrounds the brecciated fragments of 

 a marble rock. To this translucent linear interval we shall 

 return presently. 



Meanwhile, taking the " conical elongate " sac, we thus have 

 a fundus and a neck. The former, from its rounded contour, is 

 clearly defined by the translucent linear interval ; while the 

 latter, from the presence of the indigo, shows (where the sac 

 is close to the surface) that it is in direct continuation with 

 the pore by a short tubular prolongation. 



Further, it might be observed that the pore-canals branch 

 off internally so as to form a reticulation, which, following the 

 translucent linear intervals just mentioned, thus reaches the 

 oral apei-tures, as they may be termed, of the more deep-seated 

 ampullaceous sacs respectively. 



From the pore on the surface to the ampullaceous sac we 

 can thus trace the indigo and thence into the bodies of the 

 spongozoa. And that the spongozoa are the only bodies 

 which take in the indigo, may be inferred from its absence in 

 all other bodies or cells of a like kind in the structm-e of the 

 sponge. 



Here the indigo remains, and hence the easiness with which 

 we can make the demonstration. Not so, however, when the 

 undigested portions are transferred to the excretory canal ; 

 for here they are instantly discharged. Hence the difticulty 

 of following their course from the interior of the ampullaceous 

 sac to the excretory canal. In Spongilla, as before stated, I 

 have seen this take place, but have never yet been able to 

 pronounce whether the undigested particles of colouring- 

 matter are transfen'ed through the pavement-layer of spongo- 

 zoa generally or at one specialized pohit of the ampullaceous 

 sac. 



If the former, it necessitates our assuming that the whole 

 of the ampullaceous sac up to its neck is enclosed in a dilated 

 extremity of a branch of the excretoiy canal-system ; if the 

 latter, that there is a specialized point in the ampullaceous sac, 

 tantamount to an anal orifice, continuous with the branch of 

 the excretory canal. 



I incline to the latter, as being the most probable conjecture; 



