350 



THE EVOLUTION THEORY 



spherical tonii, tliat is, composed of several ids whose ' plurivalence ' 

 cannot he directl}' rccot^nized, Imt can only be inferred from their 

 further dcxclopment ; there are bivalent chromosomes of double 

 vahu- ami ([uadrivalent chromosomes of fourfold value, which we 

 lia\t' to think of as made up of two or four ids. It would lead 

 us t(Hi far to go into this moiv precisely, nor does it fall within 

 the scope and intention of these lectures to inquire into these intimate 

 and still disputed details. 



The o-erm-plasm of every species of plant or animal is thus 

 composed of a larg-er or smaller number of ids or primary constituents 

 of an individual, and it is through the co-operation of these that the 

 individual which develops from the ovum is determined. 



We have further to inquire what conception we can form of the 

 co iistitutionof a n id, and o f its mode of o ]>ei;ation. I have already 

 spoken of ' primary constituents ' {Anlagen) of which the germ-plasm 

 consists, but what right have we to think of the parts of an animal 



Fig. 88. Sperm-motlier-cells (spermatocytes) of the salamander. A, cross- 

 section of the cell in the aster-stage ; the chromosomes {chr) or idants do not 

 reveal that they are comi:)Ounded out of many ids, which are, however, quite 

 distinctly seen in B {Jcl), where the chromosomes or idants (chr) are already 

 longitudinally sjjlit. sk; cell-substance, csj}, centrosome. c, centrosome in 

 division. After Hermann and Driiner, 



as alr eady contained in the ger m_in any f orm whatevecj Is it 

 not equally possible that the germ consists of par ts, none of wh ich 

 bear aiiy3efinit6~fehition in aTtvaiice to~th e parts of the finished 

 animal 1 Miglx^^n ot the germ-^eTT, alon^_with_ Jts nucleus, un dei-go 

 transformations and regular changes whi ch would successively give 

 ri se to~"ng^ -eeaditiegs7"Tramely, the^^ fferent stages of development, 

 unt il finally the com.plete animal was attained ? 



We^^tapd Ji ere before an oldproblem, before th e_iiwa-Qpposed 

 inter pretatio ns^— the theory of ' Evolut ion ' and the th eory^ of J_Epi - 

 genesis,' which were first ranged against each other long ago, and which 

 are a cause of strife even now, although in somewhat different guise. 



The theory of ' Evolution ' is especially associated with the name 

 of Bonnet, who elaborated it in detail in the eighteenth century. 



