September 14, 1900.] 



SCIENCE. 



393 



relations might exist between the organs of 

 a plant, dissimilar as regards their function, 

 was the poet Goethe, whose observations, 

 guided by his imaginative faculty, led him 

 to declare that the calyx, corolla, and other 

 parts of a flower, the scales of a bulb, etc., 

 were metamorphosed leaves, a principle 

 generally accepted by botanists, and indeed 

 extended to other parts of a plant, which 

 are referred to certain common morpholog- 

 ical forms although they exercise difierent 

 functions. Goethe also applied the same 

 principle in the study of the skeletons of 

 vertebrate animals, and he formed the opin- 

 ion that the spinal column and the skull 

 were essentially alike in construction, and 

 consisted of vertebrae, an idea which was 

 also independently conceived and advocated 

 by Oken. 



The anatomist who in our country most 

 strenuously applied himself to the morpho- 

 logical study of the skeleton was Richard 

 Owen, whose knowledge of animal structure 

 based upon his own dissections, was un- 

 rivalled in range and variety. He elabor- 

 ated the conception of an ideal, archetype 

 vertebrate form which had no existence in 

 nature, and to which, subject to modifica- 

 tions in various directions, he considered 

 all vertebrate skeletons might be referred. 

 Owen's observations were conducted to a 

 large extent on the skeletons of adult ani- 

 mals, of the knowledge of which he was a 

 master. As in the course of development 

 modifications in shape and in the relative 

 position of parts not unfrequently occur and 

 their original character and place of origin 

 become obscured, it is difficult, from the 

 study only of adults, to arrive at a correct 

 interpretation of their morphological signifi- 

 cance. When the changes which take place 

 in the skull during its development, as 

 worked out by Reichert and Eathke, became 

 known and their value had become appre- 

 ciated, many of the conclusions arrived at 

 by Owen were challenged and ceased to be 



accepted. It is, however, due to that emi- 

 nent anatomist to state from my personal 

 knowledge of the condition of anatomical 

 science in this country fifty years ago, that 

 an enormous impulse was given to the study 

 of comparative morphology by his writings, 

 and by the criticisms to which they were 

 subjected. 



There can be no doubt that generalized 

 arrangements do exist in the early embryo 

 which, up to a certain stage, are common to 

 animals that in their adult condition present 

 diverse characters, and out of which the 

 forms special to diiferent groups are evolved. 

 As an illustration of this principle, I may 

 refer to the stages of development of the 

 great arteries in the bodies of vertebrate 

 animals. Originally, as the observations of 

 Rathke have taught us, the main arteries 

 are represented by pairs of symmetrically 

 arranged vascular arches, some of which 

 enlarge and constitute the permanent ar- 

 teries in the adult, whilst others disappear. 

 The increase in size of some of these arches, 

 and the atrophy of others, are so constant 

 for difierent groups that they constitute 

 anatomical features as distinctive as the 

 modifications in the skeleton itself. Thus 

 in mammals the fourth vascular arch on the 

 left side persists, and forms the arch of the 

 aorta ; in birds the corresponding part of the 

 aorta is an enlargement of the fourth right 

 arch, and in reptiles both arches persist to 

 form the great artery. That this original 

 symmetry exists also in man we know from 

 the fact that now and again his body, instead 

 of corresponding with the mammalian type, 

 has an aortic arch like that which is natural 

 to the bird, and in rarer cases even to the 

 reptile. A type form common to the ver- 

 tebi'ata does therefore in such cases exist, 

 capable of evolution in more than one di- 

 rection. 



The reputation of Thomas Henry Huxley 

 as a philosophic comparative anatomist 

 rests largely on his early perception of, 



