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Then the septa alter in this respect and finally in extreme parage- 

 rontic substage the approach of extinction is heralded by the close 

 approximation of several septa, as has already been stated above. 

 The greater number of these that show this change indicate that the 

 species possess great vital power and has a prolonged old age 

 changing slowly, and the small number show that senility is a more 

 rapid process. In the higher, more specialized Nautiloids and 

 Ammonoids there are usually only two or three approximate septa 

 in old age ; in Endoceras, a radical type, there may be as many as 

 twenty-two which show degeneration in the rate of growth. There 

 are other phenomena of a similar character which might be noticed 

 in this connection, but must be deferred to future publications. 



Naturalists have as a rule understood the differences between the 

 organic molecular increase that takes place within cells which is the 

 simplest form of growth, and that which follows this and builds up 

 the tissues of the body by the division of cells. Both of these pro- 

 cesses, although distinct from each other, result in additions to the 

 bulk of the whole body of the organism and come properly under 

 the head of growth. But while both are thus constructive so far as 

 the body is concerned, only one can be considered constructive or 

 anabolic while the other is essentially destructive or catabolic so far 

 as the cell itself is concerned. 



The function of nutrition and the nature of the organic structure 

 are the two essential factors of growth, and this term, /. e., growth, 

 also obviously applies to the morphology of metabolism, consisting of 

 intracellular increase, or anabolism, and cellular development, or 

 catabolism, and the phenomena resulting from the alternating 

 action of these in ontogeny. This at once shows that growth is not 

 simply progressive addition to the bulk of the body, since the mul- 

 tiplication of cells by fission is in itself catabolic or developmental 

 so far as the cells are concerned. Further than this the ultimate 

 results of catabolism are of the nature of reductions as is shown by 

 Minot's law,* and also by Maupas' observation f on the old age of 

 the agamic cycle in Infusoria and the results of late researches on 

 amitosis in cellular fission. These and the actual reduction of the 

 body taking place in extreme senility show that the term growth 



* " Senescence and Rejuvenation," Journ. Phys., xii, No. 2, 1891, and address on " Cert. 

 Phen. of Growing Old," Am. Assoc. Adv. ofSc.i, xxxix, Aug., 1890. 



t " Recherches experimental sur la multiplication des Infusores cilies," Arch, dt Zool. 

 experim. et gtn., Sr. 2, vi, pp. 165-277, et ibid., vii, pp. 149-517. 



