294 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



The copulation-determining substances are, or at least act like different 

 combinations of cis- and transcrocetin methyl esters and the proportions of 

 these two esters differ in the different races of Chlamydomonas eugametos 

 and also in certain other species of Chlamydomonas. These proportions are 

 hereditarily fixed for the gametes of these races and species ; copulation occurs 

 between those gametes of races and species in which the difference in the 

 proportions of these two esters exceeds a certain threshold value. This same 

 difference in the proportions of the esters determines also the degree of 

 chemotactic action which must precede copulation and which leads to group 

 formation in the various gametes, processes of agglutination being presumably 

 involved in these relations. The interactions between certain cells are thus 

 determined by substances which cause distance as well as contact effects and 

 they are graded in accordance with the genetic relationship of the different 

 races, and the combinations of the effective substances are likewise thus graded. 



In the alga Bryopsis, Prowazek (1907) has apparently observed, if we 

 interpret his short description correctly, that when protoplasmic particles, 

 which are surrounded by haptogen membranes, come into close contact with 

 each other, the membrane dissolves and the particles coalesce, in case we have 

 to deal with substances derived from homoiogenous organisms ; but if the 

 particles belong to different races or species, such a solution of the membrane 

 and fusion of the protoplasms do not take place. 



Similarly, in the formation of plasmodia of myxomycetae, individual 

 myxomycetae or small plasmodia first stick together and then coalesce into 

 one large Plasmodium. Occasionally such a coalescence may take place even 

 between a large active plasmodium and a small resting round plasmodium, 

 which had previously been taken into the body of the larger individual (Cela- 

 kowsky, 1892). However, as Cienkowski (1863) had found previously, only 

 plasmodia or myxamoebae of the same species can coalesce. If heterogenous 

 individuals meet, they may flow around each other but do not unite, even 

 individuals belonging to nearly related species differing in this way from 

 individuals of the same species. Whether only syngenesious or also actual 

 homoiogenous individuals coalesce with each other is not stated by these 

 authors, but it appears probable that all individuals belonging to the same 

 species can thus unite. Nevertheless, there have been observed instances in 

 which even separate parts of the same cell could not join each other; this was 

 the case when haptogen membranes developed on the surfaces of the particles. 



The tendency to react adversely to contact with the protoplasm of other 

 individuals of the same species, which has been found in certain rhizopods 

 and which we have discussed already, must have the consequence that such 

 organisms, even when not surrounded by a shell or cuticle, remain separate. 

 But if a syngenesious reaction should become identical or almost identical 

 with an autogenous reaction, then the formation of larger plasmodia or colonies 

 would not be impossible. Conversely, it may be expected that in organisms 

 which tend to form plasmodia or colonies, this sensitiveness to homoiogenous 

 protoplasm is lacking and an antagonistic reaction takes place only if more 

 pronounced differences between the organismal differentials of two individu- 



