126 0. E. Beecher — Origin and Significance of Spines. 



Growth and decline are underlain by the processes taking 

 place in individual cells as well as in aggregates of cells, for 

 spine growth must be considered in unicellular as well as mul- 

 ticellular organisms. 



Ryder 61 has very philosophically discussed the correlations of 

 volumes and surfaces of organisms, and has reached the con- 

 clusion that "the physiological function of a cell is also a 

 function of its figure, i. e., of its morphological character ; 

 that is to say, cells tend to elongate in the direction of the 

 exercise of their function." Out of this may be deduced the 

 correlative conclusion that aggregates of cells having a like 

 function also tend to elongate in the direction of the exercise 

 of this function ; and, further, it may be asserted that parts or 

 portions of cells will act in the same manner. 



A familiar illustration of these principles as applied to a 

 single cell may be taken from the Rhizopod, Amoeba proteus. 

 When disturbed by incident forces in all directions, it assumes 

 a globular form. Under continuous motion of its own, it is 

 elongated in the axis of motion, its larger pseudopodia being 

 thrust out in more or less the same direction. The presence of 

 a favorable exciting cause, like a particle of food, produces 

 extension of the protoplasm to envelop it. 



Furthermore, as is well known, continuous extra-pressure on 

 any part of an organism produces atrophy and absorption, and 

 intermittent or occasional pressure causes hypertrophy and 

 growth. That the pressure should be intermittent, seems a 

 necessary condition for hypertrophy, in order that the parts 

 affected may have normal intervals allowing the active exercise 

 of nutrition. 55 This maybe regarded as a parallel statement of 

 the law of disuse and use ; the former causing organs or parts 

 to dwindle away and lose their function, and the latter produc- 

 ing increased nutrition and growth. 



This ratio of exchange between nutrition and waste is on 

 the side of full or excessive cell-nutrition, producing growth 

 in the parts affected, while deficiency of nutrition produces 

 decline or suppression. If the successive increment constitut- 

 ing growth is along definite progressive lines towards higher 

 structures, and the decrement affects the decline of useless 

 parts or permits of the replacement of a lower by a higher 

 structure, then the sum of the changes is progressive evolution."* 



Growth, as stated, seems to require normal intervals for the 

 proper exercise of nutrition, which involves an intermittence 

 of the exciting or stimulating forces. Rhythm has been 

 shown by Spencer 6 " to be a necessary characteristic of all 

 motion, and therefore in considering either the intrinsic or 



* This is very near Cope's idea of progressive evolution. 



