BEARING OF THE NEW FACTS. 315 



Of still greater importance as regards the theory of 

 Parthenogenesis is the conclusion that from germ-cells 

 only, without any influence from sperm- cells, Polypes 

 and Medusae may be developed. Do you ask for evi- 

 dence on which to base this conclusion ? The evidence 

 is various. We have already noted the indubitable 

 fact that the unfertilised eggs of Entomostraca, gall- 

 flies, bees, moths, and silk-worms, do become developed 

 animals ; these must spring from germ-cells only. 

 Next we have the recent experiments in France and 

 Germany, which place beyond a doubt that dioecious 

 plants become fertile when their pollen is entirely 

 removed ; and we know that female plants become 

 fertile when no pollen-bearing plant is in the kingdom ; 

 so that Schleiden, in the edition of his work, The 

 Plant, just issued, says, " "VVe must now confess com- 

 plete ignorance as to the real function of the pollen.''* 

 To these may be added the fact that, according to my 

 observations, spermatozoa are rarely met with in the 

 Polypes, whereas ova are extremely abundant. 



All this evidence, however, is as nothing beside that 

 which is furnished in the very remarkable researches 

 on the reproduction of Aphides made by Professor 



* Schleiden, Die Pflame, 1858, p. 72. He draws the piquant con- 

 clusion that it is precisely in those plants on which Linnaeus founded 

 his sexual system that we have now no evidence of sexuality, whereas 

 in the cryptogamic plants sexual distinctions have been accurately 

 ascertained. It seems to me, however, that this paradox is more 

 piquant than true, and that the analogous johenomena of Partheno- 

 genesis in animals explain the difficulty, without forcing us to deny 

 the sexuality of the -Phanerogamia. 



