28 Mr. H. J. Carter on the Ultimate Structure of Spongilla. 



laceous sacs, where they remain a quarter of an hour or more, 

 until they are thrown off and find their exit through the efferent 

 system of canals. 



During their course we observe, that on arriving near the 

 ampullaceous sacs, they are rapidly drawn aside, and for the most 

 part pass into their cavities ; and by seeking for those favour- 

 ably situated for such observations, that is, at the circumference 

 of the parenchyma, we not only see that this takes place at one 

 point only, but also, frequently, that at this part of the sac there 

 is the circular aperture mentioned, and that they pass in through 

 this aperture ; further, after a certain time, we observe, that the 

 particles of carmine which have accumulated round the inner 

 surface of the sac, are gradually thrown off from its circum- 

 ference, and, falling into the efferent system of canals, are thus 

 carried away and finally ejected. 



It would have been satisfactory to have seen the particles pass 

 in through the aperture while the latter was uppermost or under- 

 most, and in the focus of the microscope (PI. I. fig. 3 a)*, but 

 this I could never do, perhaps from the rapidity with which they 

 are whirled into the interior ; but when the aperture happens to 

 be on one side of the sac, the particles may be seen to pass 

 through it into the interior, and generally to adhere to the first 

 part with which they come into contact, when they are instantly 

 enclosed by the sponge-cell on which they impinge. Again, the 

 aperture would not appear to be the only part of the exterior of 

 the ampullaceous sac which is in communication with the afferent 

 canal, but a much larger portion is bathed by the afferent fluid, 

 for particles of carmine may be seen to adhere to the external 

 surface of this sac as well as to be carried into it ; and the latter 

 seems to be more the case as the sac becomes altered from want 

 of nourishment, after having reached its maximum of develop- 

 ment under the circumstances mentioned. 



If now we clear the watch-glass of all superfluous carmine by 

 dipping it in clean water, and again place it under the micro- 

 scope, the facts to which I have before alluded will become per- 

 fectly evident, viz. that the colouring matter is wholly confined 

 to the ampullaceous sacs, and that the sponge-cells of the in- 

 vesting membrane do not contain a single particle; while, by 

 tearing the Spongilla to pieces, it will be found as much in the 

 bodies of the monociliated as in those of the unciliated sponge- 

 cells. Thus the component parts of the ampullaceous sac are 

 easily demonstrated. One point, however, remains to be proved, 



* This aperture corresponds in every respect, except the presence of the 

 tubercle, with the aperture of the investing membrane ; but I never could 

 entirely satisfy myself that the latter was not a contracting vesicle, until I 

 saw the particles of carmine pass in through it. 



