470 Dr. B,. Greef on the Structure and 



In the same colonies of which some animals bear a nucleus 

 with the above-described hair-like structures, there are others 

 the nucleus of which has retained the ordinary elongated, 

 horseshoe-like form. But on closer examination we observe, 

 even in these, very noteworthy alterations, which, when we 

 pass under review a series of different individuals, show a 

 certain gradational sequence. The first stage appears to be 

 that, in the midst of the nucleus, a clear, irregularly formed, 

 and often repeatedly interrupted longitudinal axis makes its 

 appearance (PI. XV. fig. 11). In a subsequent stage this 

 longitudinal axis is seen as a uniform cord, filled with dark 

 granules, passing through the substance of the nucleus (fig. 12), 

 so that, especially taking into consideration the following 

 structures, one is vividly reminded by it of the rhachis of the 

 Nematoda. Further investigation shows us the axial cord 

 surrounded by large pale nucleoles, which have apparently 

 sprouted from the former (fig. 13). These nucleoles constantly 

 increase in number with a gradual increase in size (fig. 14), 

 so that finally they occupy nearly the whole of the nucleus. 

 Subsequently I have fancied that I detected such nucleoles also 

 floating in the body-cavity, but have been unable to arrive at 

 any certainty upon this point. 



It is indeed very seductive to express the opinion, which 

 might be supported by many analogies with other observa- 

 tions, that the above-described phenomena in the nucleus 

 stood in connexion with the sperm atozoid-like structures in 

 the nucleus of other individuals — in other words, that we are 

 here in presence of a sexual reproduction in the Infusoria, and 

 this not merely brought about by special organs to be re- 

 garded as ovarium and testes, but even by these organs being- 

 distributed upon dififerent individuals of the same stock, so 

 that these animals are of separate sexes (monoecious). But, 

 with reference to the above remarks, I prefer in this case also 

 simply to communicate the discovery, leaving a decision upon 

 it for further investigations. 



It seems, however, to be beyond doubt that both the 

 organization and life-history, not only of the Vorticellse, but 

 of the Infusoria in general, are comparatively rich and highly 

 developed, but that only a little of it has hitherto been de- 

 ciphered with certainty — and that Ehrenberg, although he may 

 have erred much in details, especially in the interpretation of 

 the organs and structures first seen or discovered by him (and 

 this must be borne in mind), nevertheless, on the whole, 

 supported by his extended and indefatigable investigations 

 and abundant observations, has recognized with just tact and 

 acuteness the high organizational value of the Infusoria. 



