246 



some point or other must be postulated even here. However, from 

 R. Hertwig's statements the actual point can be fixed upon with a 

 fair degree of certainty, and, as will be evident, it would appear to 

 lie at a certain phase of the conjugation which a priori seems to 

 be a very likely one. 



Amoeba, Gregarina etc. — in fact a great many far simpler 

 Protozoa than Paramecium, apart from fission, exhibit a simple 

 process of conjugation, leading to encystment and spore-formation. 

 Such a process, however simple it may be, must entail a reduction 

 of chromosomes prior to the next conjugation. 



Although there appear to exist no direct observations on such a 

 reduction in these cases, there is practically no doubt that it takes 

 place at the spore-formation following conjugation and encystment. 

 Otherwise the spore-formation would be without meaning; for these 

 forms can multiply in a very rapid manner by simple fission alone. 

 Such a conjugation as the above must be a very primitive form of an 

 alternation, and, indeed, one in which a zygote or gametozooid hardly 

 can be said to possess a separate existence for any lengthy period ; 

 because the spore-formation and reduction follow almost immediately 

 on the conjugation and duplication. 



Paramecium is morphologically a far more complex organism. 

 It presents more than one nucleus, and division of labour among these. 

 As in Amoeba we recognise here two processes of multiplication, 

 fission and conjugation '). 



Colipidium colpoda (Fig. 1)^) is usually cited as affording 

 one of the simplest examples of conjugation, and it may therefore be 

 the first form to be examined. 



Turning our attention to the processes that occur after conjuga- 

 tion (/", ^, h) we find that these are all simple fissions, and they are 

 bound-up, as E. Maupas has demonstrated, with differentiations of 

 nuclei into nutritive and reproductive, and the formation of new indi- 

 viduals by fission. 



There are no abortive products , and there is no evidence of 

 spore-formation subsequent to the conjugation. 



Developmental processes which appear to be nonsensical have 

 usually a deep significance. The morphologist who encounters such 



1) Spore formatiou is not a distinct and separate mode of reproduc- 

 tion, but is a necessary corollary to conjugation. 



2) After Maukas. 



