86 SECTIONAL ADDRESSES, 



buggestion of special interest that has been made '" is that the concen- 

 tration of carbon dioxide in the atmosphere, and hence also in natural 

 waters, was very much greater than it is to-day. Free oxygen, indeed, 

 may have been entirely absent, and all the free oxygen now present in 

 the air may owe its existence to the subsequent splitting up of carbon 

 dioxide by the action of plant life. With such possibilities of differences 

 in the conditions in this and in so many other directions, may we not 

 be well satisfied if, for the time, we can say that the formation of 

 carbohydrates and proteids has been brought within the category of 

 ordinary chemical operations, which can occur without the previous 

 existence of living substance? 



To return once more, however, to the free-swimming, autotrophic 

 flagellate. In the early stages of its history the loss caused by sinking, 

 and so getting below the influence of light and the possibility of further 

 growth, must have been enormous. We may conceive a constant rain 

 of dead and dying organisms falling into the darker regions of the sea, 

 and thus a new field would be offered for the development of any slight 

 advantages whicli piarticular individuals might possess. Under such 

 conditions we may suppose that the holozoic or animal mode of nutrition 

 first began in tlie absorption of one individual by another, with which 

 it had chanced to come into contact. If the one individual were 

 more vigorous and the other moribund we should designate the process 

 ' feeding, ' and the additional energy obtained from the food might well 

 cause the individual to survive. If the two individuals wiiich coalesced 

 were both sinkmg from loss of vigour, the combined energy of the two 

 might make possible a return to the upper water layers, where under 

 the influence of light growth and multiplication would proceed, and w^e 

 should, I suppose, designate the coalescence ' conjugation,' or sexual 

 fusion. 



Other individuals, again, sinking in shallow water, would stick to 

 solid objects on the sea-floor, whilst the flagellum continued to vibrate. 

 The current produced by the flagellum under these conditions would 

 draw tov/ards the organism dead and disintegrating remains of its 

 fellows, and again we should have ingestion and animal nutrition. At 

 this stage we witness the definite passage from plant to animal life. 

 A further stage is seen when a cup-like depression to receive the incom- 

 ing particles of food is formed at the base of the flagellum, to be 

 followed still later by a definite mouth. 



Any roughening of the external surface of the swimming flagellate, 

 such as we so often find brought about by the deposition of calcareous 

 plates or siliceous spicules, or the production of ridges or furrows, would 

 tend to slow down its speed of travel, from increased friction with the 

 surrounding water. This would have a similar effect to actual fixation 

 ni drawing floating particles by the action of the flagellum, and also 

 lead to animal nutrition. Still another development would occur when 

 the fallen flagellate began to creep along the sea-floor by contractile 

 movements of the plasmic surface, losing its flagellum, and adopting 



" See Carl Snyder, 'Life without Oxygen,' Science Pioniess. vol. vi., 1912, 

 p. 107. ^ -^ ' 



