744 THE RESPIRATION AND [pt. iii 



and Kozmina, working on Ascaris, has obtained very^ similar results 

 to those of Drastich, mentioned above. On the other hand, the 

 formation of the chitinous envelope, the internal membrane and the 

 perivitelline space, and the elimination of the two polar bodies, can 

 go on normally in the absence of oxygen, as appears from the work 

 of Szwejkovska. As regards cleavage, Szwejkovska is in agreement 

 with Kozmina and with Zavadovski & Orlov, 



There is little evidence that developmental rate in any form is in- 

 creased by raising the oxygen tension or concentration. Rollat's 

 claim that silkworm eggs hatched much earlier in compressed than in 

 ordinary air was discredited by Bellati & Quajat. 



The disputed question only concerns amphibia and birds, and 

 originates from the work which Samassa did during the last decade 

 of the last century. We are not here concerned with variations in 

 the degree of susceptibility to oxygen lack or oxygen excess on the 

 part of the embryo during its development, but with the capacity 

 which it has been alleged to have of being able to live and develop 

 anaerobically in the very early stages. Samassa affirmed in his first 

 paper that the early segmentation stages of frog's eggs were ap- 

 parently independent of oxygen, and would proceed in atmospheres 

 of hydrogen and nitrogen, though gastrulation would not take place 

 under such conditions. Kept in pure irrespirable gases, they retained, 

 if unfertilised, their developmental capacity for many days, though 

 the resulting embryos were often abnormal. The experiments were done 

 in a stream of pure hydrogen, so that Samassa believed he had washed 

 every trace of oxygen out of the gelatinous egg-coverings. He next tried 

 high vacua, first by means of a mercury pump, and then a cathode ray. 

 Still they developed as far as complete blastulae. Samassa found, 

 however, that carbon dioxide had a definitely toxic action, stopping 

 segmentation, and, if pure, killing the eggs within 20 hours. (Com- 

 pare Burfield's work on the plaice egg, p. 669.) He recalled that 

 Hallez had found Ascaris eggs to be capable of living for a month 

 in pure carbon dioxide and then developing, but rightly regarded 

 a parasitic nematode as a special case. About the same time 

 Loeb reported an extreme resistance on the part of Fundulus eggs 

 to oxygen lack in the very early stages. Samassa was convinced 

 that the effects he obtained were not due to traces of oxygen, and 

 argued that, if it were so, all the eggs in a vacuum flask would hardly 

 be expected to develop synchronously, for the weakest would be 



