220 



derived from the monocytic digestive processes (Fig. 2), but on in- 

 spection of Fig, 3 and a consideration of the relationship of the vascular 

 system to the intestinal canal in such a form as Lumbricus will be 

 absorbed, not into the coelom but into the vascular space. Hence, 

 just in the proportion in which polycytic digestion predominates in 

 comparison with monocytic digestion in an organism, so the vascular 

 fluid will become more of a nutritive fluid and less of an excretory, 

 and the coelom will proportionately lose its importance, and become 

 reduced in size. 



Thus, supposing the polycytic digestion to become predominant, 

 and the food particles to be reduced to a soluble condition in the 

 enteron and absorbed polycytically through the enteric wall into the 

 vascular system, then the function of distribution of nutritive fluid 

 will be relegated to the blood or vascular fluid, the coelom will no 

 longer act in the distribution of nutritive products, and will become 

 reduced in size, its cavity will remain only in connection with the 

 sexual function, and the walls only in connection with sexual organs ^^. 

 Such a case is never seen except in the extreme degeneration of para- 

 sites, because monocytic ingestion is never quite dispensed with, — in 

 connection with the absorption of fat the monocytic ingestion appears 

 to survive even in the highest Vertebrata ^9^ though in this case also a 

 secondary adaptation (the thoracic duct) enables the monocytic in- 

 gestive cells charged with fat also to pass into the vascular system. 



The addition of a nutritive function to the blood need not 

 necessarily mean a complete change of function, for the respiratory 

 and excretory functions of blood still survive in the highest types, that 

 is to say, the function of an intermediary between the tissues and the 

 respiratory and excretory organs, but the respiratory pigment, no 

 longer difl'use, is relegated to special carriers (red corpuscles) whilst 

 the plasma becomes nutritive. A perfectly parallel case of transference 

 of function is found in the allantois whose phylogenetic history indi- 

 cates it to have acquired the function of nutrition, in addition to those 

 of excretion and respiration. 



One need not multiply facts in support of the above. The blood 

 of all the higher animals is well-known to be nutritive in function, 

 and to also subserve respiration and excretion, whilst authorities have 

 already been quoted to shew that in the lower coelomata this is not so, 



58 »In the later Molluscs the walls of the vessels have swollen out in many 



regions and have obliterated the coelom With regard to the Arthropoda, Prof. 



Lankester formulated the same view.« Nature, March 1888. 



59 Loc. cit. 



