In a general way, therefore, as Dohrn has pointed out, this principle holds good of man not only as an organic unit but as a compound organism. Degeneracy[62] is a gradual change of structures by which the organism becomes adapted to less varied and less complex conditions of life. The opposite progression process of elaboration is a gradual change of structure in which the organism becomes adapted to more and more varied and complex conditions of existence. In elaboration there is a new expression of form corresponding to new perfection of work in the animal machine. In degeneracy there is suppression of form corresponding to the cessation of work. Elaboration of some one organ may be a necessary accompaniment of degeneracy in all the others. This is very generally the case. Only when the total result of the elaboration of some organs, and the degeneracy of others, is such as to leave the whole mass in a lower condition--that is, fitted to less complex action and reaction in regard to its surroundings than is the type--can the individual be regarded as an instance of degeneracy. These degeneracies appear at varying periods, since struggles for existence on the part of the different organs and systems of the body are most ardent during periods of body evolution and involution. During foetal life, during the first dentition, during the second dentition (often as late as the thirteenth year), during puberty and adolescence (fourteen to twenty-five), during the climacteric (forty to sixty), when uterine involution occurs in woman and prostatic involution in man, and finally during senility (sixty and upwards), during all these periods degeneracy may be shown by mental or physical defect, a congenital tendency to which has remained latent until the period of stress. These defects may be such biochemic alterations (undemonstrable by existing methods) as lead to diminished inhibitory power or other altered function, or to secondary pathologic or teratologic change of decidedly demonstrable nature. Organs and structures checked at a certain phase of development may pursue a course of development differing from that pointed out in man but outlined in other vertebrates. The human cyclopean monstrosities, for example, might be regarded as reversions to the single-eyed sea-squirts, who are possibly the Ascidian precursors of the vertebrates.