(Russell, 1916, p. 268), yet the pitifully imperfect record of fossils precluded any attempt to do so directly. How fortunate then that the immediately accessible ontogenies of modern forms could reveal life's history even more faithfully. It is largely for this reason that Haeckelians insisted so strongly on the repetition of adult ancestors by descendant embryos. Early in his career, William Bateson sought phylogeny in embryology; recalling, in a sadly skeptical old age, his study of Balanoglossus under W. K. Brooks at the Johns Hopkins summer laboratories, he wrote "Morphology was studied because it was the material believed to be most favorable for the elucidation of the problems of evolution, and we all thought that in embryology the quintessence of morphological truth was most palpably presented. Therefore, every aspiring zoologist was an embryologist, and the one topic of professional conversation was evolution" (1922, p. 56).

Wilhebn His and His Physiological Embryology:
A Preliminary Skirmish

Among early opponents of recapitulation, Wilhelm His, professor of anatomy at Leipzig, was surely the most effective. He did not achieve this status by marshaling the most telling rebuttals to recapitulation; his specific arguments were, in fact, fairly weak (1874, pp. 165-176). Rather, he challenged Haeckel's methodology and asserted that the most important causes of embryological shapes were proximate and efficient. He sought to explain the complexity of developing form by displaying it as the automatic result of simple mechanical pressures produced by local inequalities of growth. He compared the embryonic layers of the chick to elastic sheets and tubes, and "constructed" the principal organs by cutting, bending, pinching and folding. In his great work of 1874, Unsere Körperform und das physiologische Problem ihrer Entstehung, His noted the extraordinary resemblance between embryonic organs and simple manipulations upon rubber tubes (Figs. 23-25). "We must start," His wrote, "from the fact that the brain, at its beginning stages, is a tube with moderately elastic walls" (p. 96). With a strong thread, His attached one end of his rubber tube to a fixed point and bent the tube toward that point (Fig. 23). He compared this with the initial attachment of the medullary tube to the foregut and invoked the same simple force as a proximate cause of morphogenesis:

The foregut plays the role of the fixed thread, and the form assumed by the anterior end of the brain [vordere Gehirnende] corresponds exactly to the paradigm. In fact, you need only compare [Figs. 23 and 24] in order to find the