132 Dr. O. Zacharias on the Reproduction and 



which might be construed as indicating an aperture ; but in 

 this endeavour I did not succeed. It even appeared that the 

 direction of oscillation was inwards, and that the cilram, 

 which beat much more violently than in Rotifer, was at- 

 tached to the upper closed end of the organ. 



I repeated my observations upon this point a few days 

 afterwards, but came again to the same result. 



Now I find from Eckstein's memoir that this naturalist 

 has made observations upon the tremulous organs of Rotifer 

 vulgaris which differ considerably from mine, and rather agree 

 with what I believe I have seen in Brachionus. I say ex- 

 pressly that for my own part I indeed entertain the conviction 

 that 1 could see nothing else in the material at my disposal ; 

 but this does not exclude the possibility that other observers 

 may have had the advantage of more favourable objects, and 

 perhaps made more numerous observations than myself. 



According to Eckstein the tremulous organs of Rotifer 

 vulgaris are of a clavate form and attached by the thinner 

 end to the lateral canals. At the upper end they are closed 

 by a hemispherical lid, to the middle of which the long 

 cilium is attached- Beneath this lid Eckstein thought he 

 detected an oval aperture, which, however, does not extend 

 to the free extremity of the cilium. In his opinion, which is 

 identical with that of Leydig, the waste fluids of the body are 

 carried from the body-cavity into the excretory ducts by the 

 vibrating cilium, passing from them into the contractile 

 vesicle, and thence outwards. 



I leave this observation to stand on the same footing that I 

 claim for my own. Eckstein certainly only states what he 

 has seen. In the presence of such diverse observations, 

 however, one may inquire into the cause of the diversity, and 

 this, in my judgment, is to be found in the influence which 

 the quicker or slower motion of the oscillatory cilium exerts 

 upon our visual organs. In Rotifer, in which the cilium 

 oscillates more slowly, I had the impression that the beaker- 

 like organ was open at the top. But in the tremulous organ 

 of Brachionus, in which the cilium shows a strong flickering 

 motion, and oscillates in short undulations, the resulting 

 motion from this, in combination with the recognition of the 

 convergent lateral contours of the organ, is that the latter must 

 be closed above. This conclusion we arrive at quite against 

 our will, because a briefly undulating cilium, projecting some- 

 what above the margin, simulates the optical section of a 

 cap-like operculum, which really does not exist. That K. 

 Eckstein has recognized a a hemispherical operculum " also 

 in Rotifer may perhaps be due to the individual constitution 



