LIFE OF ELIE METCHNIKOFF 57 



Already the observations lie had made had in 

 themselves a real importance. For instance, his 

 studies in divers specimens of the worm type, a type 

 which offers very heterogeneous forms, had permitted 

 him to establish links of continuity between certain 

 groups among them. Whilst studying those animals 

 at Giessen in 1865, he had discovered the capital fact 

 which proved to be the starting-point of all his future 

 work — ^the intercellular digestion of an inferior worm, 

 a land planarian, the Geodesmus bilineatus. He had 

 compared this digestion with that of the superior 

 Infusoria and had seen in it one more proof of the 

 genetic connection between the type of the Protozoa 

 and that of worms. 



He did not then realise the full bearing of this 

 observation, which really constituted the basis of his 

 future phagocyte theory ; this was only to appear 

 eighteen years later. 



He had also made researches on numerous speci- 

 mens of insects and on the scorpion, establishing the 

 fact that they aU had embryonic layers ; he concluded 

 that he was " entitled to extend the theory of em- 

 bryonic layers to Arthropoda." 



Finally, he had discovered embryonic layers similar 

 to those of the Vertebrates in inferior Invertebrates, 

 the Cephalopoda (Sepiola). This established a link 

 of continuity between the higher and lower animals. 



