- CHAPTER IV 



ANAEROBIOSIS AND THE ORIGIN OF 

 ENDOPARASITISM 



It was shown previously that many parasites live in 

 surroundings that are extremely poor in oxygen, or, some- 

 times, even entirely devoid of it. It is not sur^Drising, 

 therefore, that the question of the origin of the anaerobic 

 functions which these organisms exhibit has been corre- 

 lated with that of their parasitic nature. 



The first author to have suggested such a correlation 

 was Bunge (1889). According to him the worms and in- 

 sect larvae occurring within the intestinal tract of ver- 

 tebrates belong to classes of which the free-living rep- 

 resentatives show, at least in some cases, a remarkable 

 resistance in anaerobic media. He mentions in partic- 

 ular the parasitic cestodes and nematodes and, as cor- 

 responding free-living organisms, the mud-dwelling tur- 

 bellaria and nematodes. Thus the intestinal parasites 

 would be derived from free-living animals that were an- 

 aerobes before acquiring parasitic habits. Anaerobic 

 muds can, according to him, be regarded as predisposing 

 habitats ("Yorschule") for intestinal parasitism. He 

 considers it, however, as certain that the mud-dwellers, 

 and therefore ultimately also the parasitic worms, were 

 derived from aerobic ancestors. 



Bunge 's views have been rather widely quoted, but Al- 

 sterberg (1922) has raised some objections to them. He 

 points out, first, that large grouj^s of animals can usually 

 be classified so as to bring out apparent phylogenetic re- 

 lationships at the will of an author, but such classifica- 

 tion is of relatively little value. Secondly, he empha- 

 sizes that there is a rather fundamental difference in be- 

 havior between intestinal parasites and free-living in- 

 vertebrates enduring the adverse conditions of anaerobic 

 habitats. The latter, with perhaps a few exceptions, 



