ON THE VITALISTIC VIEW OF NATURE. 447 



elements concerned have both been recognised to be 

 cells, both have been found to undergo, before what is 

 termed the stage of maturity, similar preparatory changes. 

 The changes represent, as it were, the last stages of their 

 independent existence as living cells. After these 

 changes have taken place they can only enter into a 

 new cycle of existence, exhibiting new powers of growth 

 and division by a process of fusion where each supplies 

 what in the other is wanting to start on a new cycle of 

 life i.e., of differentiation and development. 



Thus the vague theories of former times, which reach 

 far into the nineteenth century, the speculations of the 

 Spermatists and the Ovists, have during the last thirty 

 years, beginning with Pringsheim's observation in 1869 

 of the pairing of the swarm-spores of certain alga3, 



tation of the purely enumerative, 

 or all-case method. The number 

 of instances in which the process 

 of fertilisation, with its various 

 preparatory stages and its conse- 

 quences, can be actually observed 

 is infinitesimally small compared 

 to the number of different species 

 and varieties in jvhich it is end- 

 lessly repeated on lines which no 

 biologist doubts to be essentially 

 the same. M. Yves Delage says : 

 " C'est une chose remarquable com- 

 bien certains etres, par des particu- 

 larites en apparence sans inteYet 

 ont facilite la solution de certains 

 problemes presque insolubles en 

 dehors d'eux. L'Ascaris meyaloce- 

 phida [the round - worm of the 

 horse, first observed by van Bene- 

 den in 1883], par le petit nombre 

 de see chromosomes, les Echino- 

 dermes [sea urchins, &c.] par la 

 facilitd avec laquelle ils acceptent 

 la fecondation artificielle, ont fait 

 faire, en dix ans, plus de progres 



aux questions relatives a la fecouda- 

 tion que n'ont fait avant ou depuis 

 tous les autres animaux re*unis. 

 Dans 1'Ascaride, le testicule forme 

 un long tube et les diverses phases 

 de la spei matogenese s'accomplis- 

 sent dans les regions differentes de 

 1'organe : il y a une zone a sper- 

 matogonies, une zone a spermato- 

 cytes en voie d'accroissement, une 

 zone ou se font les divisions re- 

 ductrices et une enfin ou les sper- 

 matides se transforment en sper- 

 matozoides" (L'He're'dite,' p. 133). 

 See on the variety of objects which 

 have lent themselves to the gradual 

 unravelling of the processes of cell 

 division, nuclear division, fusion of 

 nuclei, cleavage and embryonic de- 

 velopment, notably the volume of 

 Prof. Val. Haecker, ' Praxis und 

 Theorie der Zellen- und Befrucht- 

 ungslehre' (Jena, 1899). A very 

 lucid summary is contained in J. 

 A. Thomson's ' The Science of Life ' 

 (1899). 



