XI.] PROBLEMS OF THE DAY. 89 



individuals which are less favourably placed for the continuation 

 of the species. How, in fact, can this be otherwise, since, in 

 Infusoria, the unlimited continuance of life is bound up with 

 conjugation, just as in the ova or spermatozoa of higher 

 organisms, it is dependant on fertilization. It might be objected 

 that the cases are different, inasmuch as the germ-cells which 

 fail to be fertilized perish for lack of nourishment, while the 

 Infusoria which fail to conjugate experience no such difficulty : 

 when therefore they come to an end after a certain number of 

 generations, their death must be due to the working of other 

 causes. But in the above-mentioned Daphnid Moina rectirosiris 

 when copulation has not taken place the unfertilized egg is not 

 laid at all. It retains the very position in the ovary which it 

 would occupy during development, and it is placed under the 

 most favourable conditions of nutrition. For some time it 

 retains its vitality, but if still unfertilized, it ultimately dies and 

 undergoes dissolution, being finally completely reabsorbed by 

 the surrounding epithelial cells of the ovary. The egg is so 

 constituted that it remains alive for a certain time awaiting 

 fertilization, and then, in spite of the most favourable conditions 

 of nutrition, it perishes. If copulation be delayed in the nearly 

 allied Moina paradoxa, the unfertilized eggs are laid and die at 

 once, so that their material is lost to the animal. It is obvious 

 that the arrangement in Moina rectirosiris is a special adapt- 

 ation enabling the organism to utilize the material of the large 

 eggs which, unless fertilized, are incapable of further develop- 

 ment. We do not know what kind of an arrangement it is 

 which involves the death of the egg although surrounded by 

 such favourable conditions of nutrition, any more than we 

 know what causes the fate of the unconjugated Infusorian : the 

 facts however show that some arrangement must exist to 

 produce such results. The continued life of an egg requiring 

 fertilization, is dependant on fertilization ; that of an Infusorian 

 needing conjugation, on conjugation. 



The experiments of Maupas seem to show that Infusoria are 

 adapted for fertilization, that periodical conjugation is one of 

 the conditions of their life, like food and oxygen. But it is a 

 fallacy, only explicable on the ground of deep-rooted prejudice, 

 to argue from this that they are really mortal, and that their 

 actual immortality depends on the magic of conjugation. One 



