Mr. H. J. Carter on ihr Ultimate Structure of Spongilla. 29 



namely, that there is no direct communication between the afferent 

 canals, or the auipullaecous sacs, and the efferent canals. This 

 is easily effected by placing a little cai-minc in the water, and 

 observing the moment of its entry through the apertures of the 

 investing membrane and that of its exit through the efferent 

 tube, when the interval will be found to vary ; but as it is sel- 

 dom less than a quarter of an hour, this is quite sufficient to 

 show that there is no direct communication between these cavi- 

 ties ; while the mode of enclosing the particles by the small 

 sponge-cells being known to be like that of the Ama'bu, their 

 having been seen to throw them off at the circumference of the 

 ampullaceous sac, when they are immediately carried away by a 

 current passing through the canal into which they are thrown, 

 is still further corroborative of the fact ; but, indeed, it requires 

 no corroboration, for w^hen the sacs are only one layer deep, it 

 can be seen. 



We have now to consider by what power the particles are 

 draw^n into the ampullaceous sacs, and how a constant current 

 through the Spongilla is maintained — questions which we can 

 only hope to answer by a study of the organs of Spojigilla indi- 

 vidually ; and fortunately, as far as the first inquiry goes, this 

 is much aided by the change which takes place in the new 

 Spongilla a few days after it has been developed. 



The same difficulty which exists in maintaining life in the 

 Infusoria, viz. the want of proper nourishment, is experienced 

 with respect to the young Spongilla, and hence, sooner or later, 

 it becomes starved ; but frequently, just before this takes place, 

 the whole community of sponge-cells, more or less, separate, 

 dissolve partnership, so to speak, leave their habitation, and 

 issue forth into the watch-glass to seek independent existences 

 respectively for themselves. At this time the ampullaceous sac 

 may be seen entire, but reduced to an actinophorous form (PI. I. 

 fig. 9), and presenting a single nucleus, while in other instances 

 the community of this sac have separated, and its monociliated 

 and unciliated sponge-cells are also seen spread about the watch- 

 glass ; also groups of much smaller monociliated cells like those 

 called Uvella by Ehrenberg ; and lastly, the characteristic sponge- 

 cell of the investing membrane. 



The one, however, which interests us most here, is the mono- 

 ciliated sponge-cell of the ampullaceous sac (that which I once 

 supposed to be the androspore), and this may be seen attached 

 by a pedicular elongation of its substance to the watch-glass on 

 one side, and with its single cilium undulating on the other 

 (fig. 10). We have it now, then, exactly in the position for 

 ascertaining the direction of the currents of the latter, and these, 

 when a little carmine is added, are found to be towards the body 



