III. 6 



ATMOSPHERIC PRESSURE 



111 



TABLE XIII 



This method has given similar results for the eggs of the 

 fishes Ctenolabrus and Fundnlus (Loeb). One or two points 

 are, however, worthy of especial notice. 



The former develops at the surface of the sea, and is more 

 sensitive to a lack of oxygen than the latter, the segmentation 

 of whose egg will indeed continue for twenty-four hours in pure 

 hydrogen, though an embryo is never formed. In Ctenolabrus, 

 on the other hand, segmentation never advances further than 

 the eight-celled stage, and the cell-boundaries already formed 

 subsequently disappear, though they can be restored on removal 

 to pure oxygen. In Fundulus the capacity for enduring a lack 

 of oxygen decreases (or the need of oxygen increases) with the 

 progress of development ; the fatal exposure for a newly 

 fertilized egg is four days, for a newly formed embryo thirty- 

 two hours, for an embryo with the circulation established 

 twenty-four hours, and for the newly hatched larva shorter 

 still. Carbon dioxide is quickly fatal to both species. 



The lack of oxygen has also a noteworthy effect on the pig- 

 ment cells which are found, especially round about the blood- 

 vessels, on the yolk-sac of Fundulus. These pigment cells are 

 of two kinds, black and red, and when the embryo is deprived of 

 oxygen the former disappear, the latter diminish only a little. 



