98 DR. ELIAS METSOHNIKOFF. 



a simple explanation of such appearances as the transformation 

 of the degenerating nervous system into a heap of blood-cor- 

 puscles, which is at present believed to be due to a direct 

 morphogenetic change in the ganglion cells. 



It may here be pointed out that Ganin, in 1876, attributed 

 to amoeboid mesoderm cells an important part in the so called 

 histolysis of muscle- fibres in flies.^ He says: *' During the 

 early stages of development I have often seen free amoeboid 

 mesoderm cells in the cavity of the foot attach themselves to 

 the surface of a muscular mass^ into which they often bored 

 deeply, appearing to nourish themselves from the substance of 

 the larval muscle.'^ Viallanes, the latest student of histolysis,^ 

 has not sufficiently considered Ganin's observations. Though 

 the very few drawings which he gives point strongly to the 

 conclusion that there is a considerable ingestion of food by 

 mesoderm cells during metamorphosis, he expresses himself in 

 his text in favour of a totally different view. Thus, he describes 

 as " degenerated blood-cells, like pus-corpuscles," elements 

 which have probably only loaded themselves with albumin 

 granules ; while his " cellules musculaires," arising out of 

 muscular debris, are also, in all probability, nothing but over- 

 loaded mesoderm cells. 



Though this ingestive power of the mesoderm is specially 

 pronounced during metamorphosis, it occurs on other oc- 

 casions. In 1880 Schneider^ showed that resorption of the 

 generative products by amoeboid cells resembling blood-cor- 

 puscles occurred in Hirudinea; an observation which I have 

 repeated for Aurelia aurita. Many of the ovarian ova of this 

 medusa become surrounded by amoeboid cells, and completely 

 devoured. These cases can be compared with the following, 

 which have been observed by me. If a Pilidium be left for 

 some time in a watch-glass, the rudimentary nemertine 



' ' Beitrage zur Kentuiss der postembryonalen Entwickelung der Insecten.' 

 Warscbau, 1876 (Russian). 



2 " Recherches sur I'histologie des Insectes." ' Ann. Sci. Nat,,' v, xiv, 1882, 

 pp. 135—158. 



^ " Ueber die Auflosung der Eier und Spermatozoen in den Geschlecbts» 

 organen." ' Zool. Anz.,' 1880, p. 19. 



