356 PROVISIONAL HYPOTHESIS Chap. XXVII. 



in the case of the Teredo, 12 as did formerly Prevost and Dumas 

 with other animals, that more than one spermatozoon is 

 requisite to fertilise an ovum. This has likewise been shown 

 by Newport, 13 who proved by numerous experiments, that, 

 when a very small number of spermatozoa are applied to the 

 ova of Ba'trachians, they are only partially impregnated, and 

 an embryo is never fully developed. The rate also of the 

 segmentation of the ovum is determined by the number of the 

 spermatozoa. With respect to plants, nearly the same results 

 were obtained by Kolreuter and Gartner. This last careful 

 observer, after making successive trials on a Malva with 

 more and more pollen-grains, found, 14 that even thirty grains 

 did not fertilise a single seed ; but when forty grains were 

 applied to the stigma, a few seeds of small size were formed. 

 In the case of Mirabilis the pollen grains are extraordinarily 

 large, and the ovarium contains only a single ovule ; and 

 these circumstances led Naudin 15 to make the following 

 experiments : a flower was fertilised by three grains and 

 succeeded perfectly ; twelve flowers were fertilised by two 

 grains, and seventeen flowers by a single grain, and of these 

 one flower alone in each lot perfected its seed : and it deserves 

 especial notice that the plants produced by these two seeds 

 never attained their proper dimensions, and bore flowers of 

 remarkably small size. From these facts we clearly see that 

 the quantity of the peculiar formative matter which is 

 contained within the spermatozoa and pollen-grains is an all- 

 important element in the act of fertilisation, not only for 

 the full development of the seed, but for the vigour of the 

 plant produced from such seed. We see something of the 

 same kind in certain cases of parthenogenesis, that is, when 

 the male element is wholly excluded ; for M. Jourdan 16 



12 ' Annales des Sc. Nat.,' 3rd series, Weijenbergh also raised ('Nature,' 

 1850, torn. xiii. Dec. 21, 1871, p. 149) two successive 



13 'Transact. Phil. Soc.,' 1851, pp. generations from unimpregnated. fe- 

 196, 208, 210 ; 1853, pp. 245, 247. males of another lepidopterous insect, 



14 'Beitrage zur Kenntniss,' &c, Liparis dispar. These females did 

 1844, s. 345. not produce at most one-twentieth 



15 'Nouvelles Archives du Mu- of their full complement of eggs, and 

 skm,' torn. i. p. 27. many of the eggs were worthless. 



16 As quoted by Sir J. Lubbock in Moreover the caterpillars raised from 

 "Nat. Hist. Review' 1862, p. 345. these unfertilised eggs "possessed far 



