]48 LIFE AND DEATH. 



It is impossible to accept Gotte's conception of the germ (Keim), 

 and at this point the question arises as to its true meaning. I 

 should propose to include under this term every cell, cytode, or 

 group of cells which, while not possessing the structure of the 

 mature individual of the species, possesses the power of developing 

 into it under certain circumstances. The emphasis is now laid 

 upon the expression development, which is something opposed to 

 simple growth, without change of form. A cell which becomes 

 a complete individual by growth alone is not a germ but an 

 individual, although a very small one. For example, the small 

 encapsuled Heliozoon, which arises as the product of multiple 

 fission, is not a germ in our sense of the word. It is an individual, 

 provided with all the characteristic 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 Mono- 

 plastides. There is nevertheless, in my opinion, a profound and 

 significant 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 Mono- 

 plastides are entirely of secondary origin, and have never formed 

 the phyletic origin of the species in which they are found. For 

 instance, the spore-formation of the Gregarines resulted from a 

 gradually increasing process of division, which was concentrated 

 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 

 animals, 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 l , it would not divide at all, 



1 These assumptions can be authenticated among the Infusoria. The encysted 

 Colpoda cucullus, Ehrbg. divides into two, four, eight, or sixteen parts ; Otostoma 

 Carteri, into two, four, or eight ; TiUina magna, Gruber, into four or five ; Lagynus 

 sp. Gruber, into two ; Amphileptus mdeagris, Ehrbg. into two or four. The last two 

 species and many others frequently do not divide at all during the encysted con- 

 dition. But while any further increase in the number of divisions within the cyst 

 does not occur in free-swimming Infusoria, the interesting case of Ichthi/ophthirhm 

 muUifiliis, Fouquet, shows that parasitic habits call forth a remarkable increase in 



