PII vsioLodiCAL EFFECTS OF LACK OF OXYGKN M 



supplied to them. Wo found before tliat a lack of oxygen 

 docs not retard cleavage as long as cleavage is at all possible. 

 In the same way an excess of oxygen does not accelerate the 

 process. 



VI II. EFFECT OF LACK OF OXYGEN ON THE CLEAVAGE OF 



THE FUNDULUS EGG 



The eggs of Ctenolabrus have a lower specific gravity 

 than sea-water, and therefore float at the surface of the 

 water. Here they find the oxygen necessary for their devel- 

 opment. If the eggs of Ctenolabrus with their great need 

 for oxygen had a specific gravity large enough to cause them 

 to sink to the bottom, they could scarcely develop in many 

 places, since at the bottom of the ocean where processes of 

 putrefaction are going on, the tension of oxygen is much 

 less than at the surface. We may therefore expect, in gen- 

 eral, that fish eggs which sink to the bottom of the ocenn 

 and develop there are much more independent of oxygen 

 than the egg of Ctenolabrus. This is really often the case. 

 The egg of Fuiidulus has a greater specific gravity than sea- 

 water and develops at the bottom of the ocean. I have shown 

 that the egg of Fundulus can develop for some time in the 

 absence of oxygen. In these experiments the eggs were 

 introduced witli a few drops of sea-water into a small glass 

 tube sealed at its lower end, and this tube was put into a 

 test-tube containing several cubic centimeters of an alkaline 

 pyrogallol solution. The test-tube then was sealed at the 

 top. The pyrogallol solution was prepared according to 

 Hempel's directions, and the oxygen must have been ab- 

 sorbed in a short time. Nevertheless, the eggs not onl\ 

 segmented, but they developed as far as normal eggs do in 

 about fifteen hours after fertilization. A large blastoderm 

 was formed which spread over a great part of the surface 



n gg ' 



