80 SURVEY OF INVERTEBRATES 



One would expect that in the natural, free-living devel- 

 opmental stages the helminths will not be injured by oxy- 

 gen of normal tension. On the other hand certain life 

 activities of parasitic stages may be inhibited if the ani- 

 mals are exposed to much more oxygen than is normally 

 present in their surroundings. The experiments of Stoll 

 ( 1940) are especially significant in this regard. He found 

 that the first parasitic ecdysis of Haemonchus contortus, 

 which occurs at the end of the third larval stage, is dis- 

 tinctly favored, in bacteria-free cultures, if the oxygen 

 supply of the medium is limited. 



B. Type of life in normal habitat. Only worms occur- 

 ring in the intestinal tract (inclusive of bile ducts) and 

 the tissue parasites will be discussed here; helminths 

 living in the lungs, in the trachea, in the swim-bladder or 

 similar habitats will, as a rule, have access to an abun- 

 dant supply of oxygen and will live aerobically, 



(a) Intestinal worms. It has been regard- 

 ed as axiomatic for many years that intestinal worms are 

 truly anaerobic animals. It was assumed that they would 

 not make use of oxygen even if they had access to it 

 (e.g., Weinland, 1901, 1913; Weinland and von Brand, 

 1926) ; occasionally the opinion has even been expressed 

 that oxygen wbuld be toxic to them (Jordan and Hirsch, 

 1927). This view can no longer be held in its old form; 

 all recent investigations (Alt and Tischer, 1931; Adam, 

 1932 ; Harnisch, 1933a ; 1937a ; von Brand, 1934a ; Kriiger, 

 1936, 1937) have shown that intestinal helminths do util- 

 ize oxygen when it is offered to them. 



Some investigators (Slater, 1925 ; Mueller, 1929; Adam, 

 1932; Davey, 1937, 1938) maintain that the animals live 

 aerobically in the intestine, but they are not too specific 

 in answering the question as to where the necessary oxy- 

 gen for an aerobic metabolism comes from. 



The present author discussed the metabolic relation- 

 ships of intestinal worms in some detail in a previous 



