76 SURVEY OF INVERTEBRATES 



of Eustrongylides ignotus up to almost a year in labora- 

 tory conditions. 



In none of these experiments was oxygen excluded, 

 although in some cases, for example, in Hoeppli and 

 Chu's (1937) investigations, the oxygen supply was 

 rather limited. It is quite apparent that the above hel- 

 minths and others that will be mentioned later are not in- 

 jured by oxygen. Since these experiments were not per- 

 formed to gain an insight into the anaerobic functions of 

 the worms, no comparative study of aerobic and anaerobic 

 survival was made. 



(b) Experimental data. Some data on 

 anaerobic survival of helminths are available. They have 

 been gathered in Table' 11, and when experiments were 

 performed under both anoxic and aerobic conditions 

 two figures are given. It is evident that small differ- 

 ences in technique play a great role in the determination 

 of the survival times. Only data gathered with one 

 and the same procedure can be rightly compared. For 

 this reason the data of workers who studied only the 

 aerobic survival have not been included. 



In almost all the experiments summarized in Table 11 

 the worms were kept in non-nutrient solutions, and bac- 

 terial contaminants were invariably present except prob- 

 ably in the case of Trichinella larvae. These two fac- 

 tors may largely account for the short survival periods 

 observed under both anaerobic and aerobic conditions. 

 The presence of bacteria is an especially important factor 

 that occupies more and more the attention of the inves- 

 tigator. It seems that even the bacteria which develop 

 in non-nutrient solutions, and which find perhaps a suit- 

 able medium in the excreta of the worms, shorten the life 

 of the latter considerably. The case of the larva of 

 Eustrongylides ignotus illustrates this point. Its max- 

 imal aerobic survival is listed in Table 11 as 19 days. 

 Recently, however, the present author, in collaboration 

 with W. F. Simpson, maintained a series of these lar- 



