264 THE UNFERTILISED EGG AS A [pt. hi 



wrongly by Schafer. However, Thunberg in 1902 conclusively 

 demonstrated the error of the belief, and showed experimentally 

 that water would pass through the membranes equally well both ways, 

 though he found that of the two the inner one was the less permeable. 

 In the case of water birds, there is evidence that the shell is absolutely 

 impermeable to water; Loisel, for instance, found that the eggs of 

 the grebe, Podiceps cristatus, and the duck, Anas domesticus, when 

 placed in distilled water absorbed not a trace of it, and gave out 

 no chloride to it over a period of many hours. The eggs of the 

 ordinary hen, on the other hand, increased considerably in weight 

 and allowed some chloride to pass out into the water. At the same 

 time, Loisel found that hen's eggs develop quite normally, at any 

 rate up to the seventh day, even if they are lying in water. This 

 experiment of Loisel's was confirmed by Lippincott & de Puy, who 

 succeeded in hatching chicks from eggs incubated while lying in | in. 

 of distilled water. The differences between these eggs and the controls 

 suggested that the eggs lying in the water not only failed to lose as 

 much water through evaporation as eggs incubated under ordinary 

 conditions, because of the limitation of the evaporating surface, 

 but actually absorbed some water. Trials with rhodamine red and 

 methylene blue demonstrated penetration by these dyes, extending in 

 the former case to vital staining of the embryo. It is known (Rizzo) 

 that the avian egg-shell has many pores (o-86 to 1-44, average 1-23 

 per sq. mm.). 



As regards gases, the only paper is that of Hiifner. Hiifner placed 

 small pieces of egg-shell with their membranes in a diffusiometer, 

 and measured the rate at which gases passed through the obstacle. 

 He found that oxygen diffused through with most difficulty, then 

 nitrogen, then carbon dioxide, and, finally, hydrogen most easily. 

 It may be significant that carbon dioxide would thus appear to be 

 able to escape somewhat quicker than oxygen can enter. But under 

 normal atmospheric pressure the amount diffusing through the whole 

 egg-shell (goose) per second was 2-115 c.c. of oxygen and 0-503 c.c. 

 of carbon dioxide. The diffusion velocity was always proportional 

 to the partial pressure of the gases, and the removal of the inner 

 membrane made no difference at all, suggesting that the principal 

 barrier was the amorphous calcium carbonate layer. It would 

 be very desirable to repeat these observations with more modern 

 methods, and on a greater variety of eggs. 



