SURVEY OF INVERTEBRATES 83 



and that, in nature, the anaerobic phase of the metabol- 

 ism is of greater importance than appears from the ex- 

 periments of Stannard, McCoy and Latchford. 



An aerobic existence within the intermediate host can 

 definitely be expected in the case of the larval Eustrongy- 

 lidcs ignotus. The animals are blood-red due to the pres- 

 ence of haemoglobin in their body fluid (von Brand, 

 1937a). If they are exposed experimentally to anaerobic 

 conditions they accumulate a considerable oxygen debt 

 which is repaid if the animals are kept subsequently in 

 an oxygen-rich atmosphere. Worms, however, that have 

 been isolated freshly from fish exhibit only a trace of 

 this phenomenon. Such a behavior indicates that they 

 had lived aerobically within the fish for if they would have 

 lived anaerobically one would expect them to have to 

 repay a maximal oxygen debt once they have access to 

 large amounts of oxygen (von Brand, 1942). 



An aerobic or primarily aerobic existence can prob- 

 ably also be assumed for many tissue helminths parasi- 

 tizing invertebrates. The clearest evidence that this as- 

 sumption is well-founded — evidence, however, which does 

 not yet constitute real proof — has been found by Vogel 

 and von Brand (1933) in the case of the developmental 

 stages of the liver fluke Fasciola Jiepatica. The metab- 

 olism of the adult fluke is anaerobic, one of the endprod- 

 ucts being higher fatty acids demonstrable in the excre- 

 tory system (von Brand and Weinland, 1924). Vogel 

 and von Brand show^ed that this excretory fat begins to 

 appear only when the parasites reach the vertebrate host, 

 probably because they there encounter oxygen deficien- 

 cies. In the stages parasitizing the snail no trace of such 

 fat could be found, a condition which apparently indi- 

 cates other, perhaps aerobic metabolic processes. 



On the other hand, there are indications of an anaero- 

 bic existence for some tissue helminths. Coutelen (1931) 

 observed fat in the excretory system of Echinococcus sco- 



