150 LIFE AND DEATH. [III. 



marks of its species, and it has only to protrude the retracted 

 processes (pseudopodia) and to take in the expelled water 

 (formation of vacuoles) in order to become capable of living in 

 a free state. In this sense of the word, germs are not confined 

 to the Polyplastides, but are found in many Monoplastides. 

 There is nevertheless, in my opinion, a profound and signifi- 

 cant difference between the germs of these two groups. And 

 this lies not so much in the morphological as in the develop- 

 mental significance of these structures. As far as I have been 

 able to compare the facts, I may state that the germs of the 

 Monoplastides are entirely of secondary origin, and have never 

 formed the phyletic origin of the species in which the}^ are found. 

 For instance, the spore- formation of the Gregarines resulted 

 from a gradually increasing process of division, which was con- 

 centrated into the period of encystment ; and it was induced 

 by a necessity for rapid multiplication due to the parasitic life 

 and unfavourable surroundings of these animals. If Gregarines 

 were free-living anim.als, they would not need this method of 

 reproduction. The encysted animal would probably divide 

 into eight, four, or two parts, or perhaps, like many Infusoria \ 

 it would not divide at all, so that the whole reproduction would 

 depend on simple fission alone during the free state. 



The original mode of reproduction among the Monoplastides 

 was undoubtedly simple fission. This became connected with 

 encystment, which originally took place without multiplication ; 

 and only when the divisions in the cyst became excessively 

 numerous did such minute plastids appear that a genuine pro- 

 cess of development had to be undergone in order to produce 

 complete individuals. Here we have the general conception of 

 the germ as I defined it. Its limitations are naturally not very 

 sharply defined, for it is impossible to draw an absolute dis- 



^ These assumptions can be authenticated among the Infusoria. The 

 encysted Colpoda cuadlus, Ehrbg. divides into two, four, eight, or sixteen 

 parts ; Otostoma Carteri, into two, four, or eight ; Tillina magna, Gruber, 

 into four or five; Lagynus sp. Gruber, into two ; Arnpliilepttis nieleagris, 

 Ehrbg. into two or four. The last two species and many others fre- 

 quently do not divide at all during the encysted condition. But while 

 any further increase in the number of divisions within the cyst does not 

 occur in free-swimming Infusoria, the interesting case oilchthyophthirhts 

 niultifiliis, Fouquet, shows that parasitic habits call forth a remarkable 

 increase in the number of divisions. This animal divides into at least a 

 thousand daughter individuals. 



