AjiipuUaceous Sac in the 8pongida. 207 



entire, and in situ. Under these circumstances, when a 

 water-canal is selected for observation which has been cut 

 across horizontally so that the eye can be directed into it per- 

 pendicularly, one or more arapullaceous sacs may frequently 

 be seen on the confines of the canal in such a position as to 

 show that the greater part of the globular ampuUaceous sac 

 is imbedded in the substance of the sponge immediately under 

 the lining membrane of the canal, while the circular aperture 

 opens on a level with it, so that as the water containing the 

 nutritive particles is rapidly carried along them, the latter 

 could be easily deflected from their course and drawn into 

 the arapullaceous sac, while the refuse or unassimilated parts 

 might be discharged through the same aperture, just as 

 takes place in a polyp. 



Comparatively thick slices thus treated show the position 

 of the arapullaceous sac more satisfactorily than microscopic 

 thin slices mounted in balsam under compression, especially 

 in the specimen under consideration, wherein their position is 

 rendered additionally clear by not being overcrowded, although 

 both processes have their advantages. 



Now I know that in Dr. Huxley's ' Introduction to the 

 Classification of Animals ' (1869) a " hypothetical section 

 of SpongiUa''^ is given (p. 15, fig. 4), wherein the current 

 of water is made to pass in at the pores and through the 

 medium of the subderraal cavity to reach the arapullaceous 

 sac by a canalicular extension of this cavity, after which it 

 makes its exit by a sirailar opening on the opposite side of 

 the sac into an excretory canal, as if the pores were specially 

 intended for the arapullaceous sacs, that is for the nutritive 

 departraent. While what I have endeavoured to show is, 

 that the pores are as ranch for the general circulation or 

 respiratory function as for the introduction of nutriment, and 

 that the arapullaceous sac, being situated on the surface of the 

 excretory canals, only requires a single aperture to tulfil its 

 function. 



I am also aware that Dr. F. E. Schulze has always inclined 

 to the view that the arapullaceous sac has two openings, 

 viz. one for bringing in the water and the other for discharg- 

 ing it, as may be seen by one of his latest illustrations (' Der 

 Badeschwamm :' Illus;rirte Deutsche Monatshefte, 1882, 

 p. 198, fig. 8), as well as in all those of his previously stained 

 and raicrotoraized preparations of the fleshy and horny sponges 

 published in the ' Zeitschrift f. wiss. Zoologie.' Moreover, in 

 some there is more than one aperture in addition to the large 

 circ 



avar 

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