742 THE POPULAR SCIENCE MONTHLY. 



logically, to worms. Further he has essentially enlarged our knowl- 

 edge of the important group of Tunicata by his researches on the 

 Ascidians, Appendicularia, Pyrosoiua, Doliolum, Salpa, etc. 



Many important advances in the morphology of the Mollusca and 

 Arthropoda are also due to him. Thus, e. g., he has greatly elucidated 

 the controverted subject of the homology of regions of the body in 

 the various classes of Mollusca. He has considered the generation of 

 vine-fretters from quite a new point of view, based on his " genealogi- 

 cal conception of animal Individuality." But it is the comparative 

 anatomy and classification of the Vertebrata which, during the last 

 ten years, he has especially studied and advanced. His excellent 

 " Lectures on the Elements of Comparative Anatomy " afford abun- 

 dant proof of this, to say nothing of his numerous important mono- 

 graphs, especially those on living and extinct fish, amphibians, rep- 

 tiles, birds, and mammals. 



Huxley's works on the comparative anatomy of the Vertebrata are 

 the only ones which can be compared with the otherwise incomparable 

 investigations of Carl Gegenbaur. These two inquirers exhibit, par- 

 ticularly in their peculiar scientific development, many points of rela- 

 tionship. They both belong to that small circle of morphologists 

 which is marked by the names of Caspar Friedrich Wolff, George 

 Cuvier, Wolfgang Goethe, Johannes Mtiller, and Carl Ernst von 

 Baer. 



More important than any of the individual discoveries which are 

 contained in Huxley's numerous less and greater researches on the most 

 widely different animals, are the profound and truly philosophical con- 

 ceptions which have guided him in his inquiries, have always enabled 

 him to distinguish the essential from the unessential, and to value special 

 empirical facts chiefly as a means of arriving at general ideas. Those 

 views of the two germinal layers of animals which were published as 

 early as 1849 belong to the most important generalizations of compar- 

 ative anatomy ; they already contain in germ the idea of the " perfect 

 homology of the two primary germinal layers through the whole 

 series of animals (except protozoa)," which first found its complete 

 expression, a short time since, in the " Gastrsea theory ; " also his re- 

 searches on animal individuality, his treatment of the celebrated ver- 

 tebral theory of the skull, in which he first opened out the right track, 

 following which Carl Gegenbaur has solved in so brilliant a manner 

 this important problem, and, above all, his exposition of the Theory 

 of Descent and its consequences belong to this class. After Charles 

 Darwin had, in 1859, reconstructed this most important biological 

 theory, and, by his epoch-making theory of Natural Selection, placed 

 it on an entirely new foundation, Huxley was the first who extended 

 it to man; and, in 1863, in his celebrated three lectures on "Man's 

 Place in Nature," admirably worked out its most important develop- 

 ments. With luminous clearness and convincing certainty, he has 



