I. Haeckel and His Opponents

“All formation, whether consisting in cleavage, in the formation of folds, or in complete separation, follows as a consequence from this fundamental law.” The law of growth brings into existence the two pairs of limbs as follows: “Their disposition is determined, like the four corners of a letter, by the crossing of four folds which limit and bound the body.” His rejects any help drawn from the history of the species, with the following justification: “When the history of development for any given form has thoroughly fulfilled the task of its physiological deduction, then it may rightly say of itself that it has explained this form as an individual form” ( cp. His, Unsere Körperform und das physiologische Problem ihrer Entstehung). In reality, however, nothing whatever has been accomplished by such an explanation. For the question still remains: Why do different forces of growth work at different spots in the germ? They are simply assumed by His to exist. The explanation can only be seen in the fact that the relations of growth of the individual parts of the germ have been transmitted by inheritance from the ancestral animals, that therefore the individual organism runs through the successive stages of its development because the changes which its forefathers have undergone through long ages continue to operate as the cause of its individual becoming.