BIOCHEMICAL EVOLUTION 



335 



haemoglobin synthesis as it was present in their Annelid ancestors possess- 

 ing this synthetic mechanism. Also too, chlorocruorin is a close isologue 

 of Annelid haemoglobin and possesses many similar properties. The haem 

 of chlorocruorin, or chlorocruorohaem, differs from protoporphyrin in 

 only a small detail, the oxidation of vinyl group 2. As for the protein 

 portion, it is very similar to that found in Annelid haemoglobin as the data 

 assembled in the following table show : 



Table XXIII 



In the case of chlorocruorin, we have a chemical entity isologous to 

 haemoglobin and present in classes of our systematic classification and the 

 comparative morphology of these classes shows their phylogenic relation 

 to other classes the blood of whose members contains haemoglobin. Here 

 we can speak of evolution of a biochemical component. In a case of this 

 type there is not only isology, but phylogenic isology, or to use a term 

 proposed by Lankester, homogeny. 



Biochemical Parallelism 



When isologous biochemical constituents are present in categories of 

 the systematic classification not phylogenically related, we say that there is 

 parallelism. The occurrence of haemoglobin in the Molluscs and in the 

 Echinoderms is an example of parallelism. In fact, parallelisms are evidence 

 for the unity of the general biochemical plan on which organisms are 

 constructed. 



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Pedersen, K. O. (1933). Koll. Z., 63, 268. 



Roche, J. and Jean, G. (1954). Bull. Soc. Chim. Biol., 16, 769; and Roche, J. and 



MouRGUE, M. (1941), Bull. Soc. Chim. Biol, 23, 1329. 

 SvEDBERG, T. (1933). X Biol. Chem., 103, 311. 

 SvEDBERG, T. (1939), Proc. Roy. Soc, Ser. B., Ill, 1. 

 VAN Slyke, D. D., Hastings, A. B., Heidelberger, M. and Neill, J. M., (1922). 



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