IMMORTALITY OF PROTOZOA 203 



were rejuvenated and started on a new cycle of activity by the 

 commingling of the nuclear material of two simple cells. 

 Further than this we see a close parallel in the manner in 

 which the nuclear material is halved, before fertilisation, by the 

 formation of the polar bodies, or by the division of the sperma- 

 tocytes in the Metazoan ovum and spermatozoon and the 

 similar formation of the polar bodies in Monocystis and Actino- 

 sphaerium, or the division of the micronucleus with the abortion 

 of all but one of its products in Paramecium. The alternation 

 of generations, so obvious in many Protozoa, would seem to 

 be masked in the Metazoa by the coherence and integration of 

 the cell progeny of the fertilised ovum. 



Thus the ovum and spermatozoon might be regarded as the 

 sexual generation of cells, the tissue-cells derived from them 

 as the numerous asexual generations, and the cycle is com-, 

 pleted on the reappearance of the ovum and spermatozoon. 

 Such comparisons open up a wide field of inquiry, the interest 

 in which is further increased when one studies the parallel 

 series of events in plants ; and the gradations exhibited by 

 Pandorina, Eudorina, and Volvox seem to supply a real basis 

 to speculation. But at present the whole subject is too obscure 

 to be discussed with profit. It must not be forgotten that no 

 process of conjugation has yet been observed in Amceba and 

 Euglena ; that the fusion of the amcebulae to form the plas- 

 modium of Badhamia is not an act of conjugation, for there is 

 no fusion of nuclei ; and that, in Actinosphaerium, the gametes 

 are the identical pairs of so-called secondary cysts formed by the 

 binary division of the primary cysts, modified only to the extent 

 of their having ejected part of their nuclear matter in the form 

 of polar bodies. Amongst so many seeming contradictions it is 

 impossible to lay the foundations of a solid theory. 



Much has been said of late years of the potential immortality 

 of Protozoa. But the facts described for Polytoma and Para- 

 mecium, as well as those about to be described for Vorticella, 

 show that these creatures, like the higher forms of life, are 

 subject to the inexorable laws of decay and death. If it should 

 be established beyond doubt that Amoeba (or any other 

 Protozoon) is capable of multiplying itself indefinitely by binary 

 division, without loss of functional activity calling for repair by 

 means of conjugation, then indeed it could be said that these 

 organisms are immortal in that decay and death would not 



