184 THE AMERICAN MONTHLY [July, 



Although I have not actually seen minute streams issuing 

 from the extremity of each villus, there can be but little doubt 

 that streams do so issue. If the limiting membrane is pierced 

 by apertures they must be infinitely more minute than are the 

 secondary apertures in any known diatom ; and the proper con- 

 ditions for demonstrating the perforations, if they exist, cannot 

 be made, as they can be made with a diatom ; yet the sudden 

 protrusion of the nipple-like processes with the hypothetical 

 aperture at the extremity of each, is precisely what reason would 

 suggest as the result of the rapid movement of a cribriform ves- 

 icle, the enclosed fluid being restrained in the rear by the re- 

 sisting body-substance. The amount of liquid in the vacuole 

 is small, and although the internal force that protrudes the villi 

 seems, under the microscope, to be comparatively great, it must 

 of course be exceedingly slight. Yet it is great enougli to pro- 

 duce a surprising change in the appearance of the external sur- 

 face. 



Dr. Leidy, speaking of the contractile vesicle of Actinophrys 

 sol, says : " Gradually expanding, it rises as a film of granular 

 protoplasm, which, becoming thinner and thinner, finally bursts 

 and gives exit to the liquid contents." In reference to the two 

 vacuoles of Actinosphaerium eichhornii he says : "On reaching the 

 full degree of expansion, they rather abruptly collapse, and ex- 

 pel the liquid contents." And the new edition of "Carpenter," 

 referring to the contractile vesicle of Actinophrys, says: " The 

 cavity of this saculus is not closed externally, but communi- 

 cates with the surrounding medium, — not, however, by any dis- 

 tinct and permanent orifice, the membraniform wall giving way 

 when the vesicle contracts, and then closing over again." 



The vesicles of Actinophrys do not burst. From what I have 

 repeatedly observed and have here described, I am convinced 

 that there is no such action. If rupture actually took place, it 

 could be readily seen, since the vesicle is large; in Actinosphx- 

 rium eichhornii it should be noted with much greater ease as the 

 organs are there still larger. But what does take place is the 

 sudden protrusion of the nipple-like processes, with apparently 

 the forcible ejection of the vacuole's liquid contents through 

 them. 



With the Infusoria it is not always possible to demonstrate 

 the existence of a passage from the contractile vesicle to the 



