xxii CONTENTS OF VOL. I. 



Note: Anomalies of Development: — Metamorphosis of Sitaris— Development of 

 Echinoderms — Pseudembryo — Peculiarity of that of the star-fish — Pseud- 

 embryos aud larvse Pp- 252 — 277 



CHAPTER XXII. 



CLASSIFICATION. 



Classification depends on Embryology— "What is meant by the facts of classifica- 

 tion—Questions of classification are real— Questions of classification which are 

 merely verbal — Position of lepidosiren— The value of any character in classi- 

 fication depends on being an index to others— Value in classification of rudi- 

 mentary organs, and of organs not connected with special habits — The develop- 

 ment theory explains all this— AfSnity means kiudred ; as of Cirrhipedes to 

 Crustaceans— Groups within gi-oups— How far the development theory is proved 

 — Reason of importance of rudimentary organs : of embryonic characters : of 

 the flower — Origin of organic forms by the accumulation of variations — Diver- 

 gent lines of variation — Divergence and re-divergeuee — Classification is gene- 

 alogy—No reunion after divergence — Metamorphosis generally is progress — 

 Exception in Cirrhipedes— Specific change also is generally progress— Groups 

 are generally united by their lower members— Animal and vegetable kingdoms 



Their probable common origin— No absolute distinction between them — .Their 



highest forms are totally unlike— Affinities of Alga-, Lichens, and Fungi : of 

 fishes and air-breathing Vertebrata— Retrograde change— Acari—Annulosa — 

 Their lower limit is indefinite, their higher groups have a definite character — 

 Annelids— Arthropoda, descended from Annelids— Number of segments in head 

 and body of Arthropods— Acari, though the lowest Arthropods, do not revert 

 to the worm-type — Pygnogouidse — Classification in a single series is impossible 

 — " Natm-a non facit saltum " — The whole of one group is seldom higher than 

 the whole of a kindred group — Organic afiinities seem like a net work — I believe 

 they are in form like a tree — Groups never re-unite after diverging — Affinities 

 will probably never be perfectly traced— Many links have been discovered, and 

 some apparent links have been found not to be real ones — Whale tribe-^Lost 

 links — Affinity is distinct from resemblance— Analogy of human kindreds- 

 Why is there organic progress? — An exhaustive classification would include 

 not only species but individuals. 



jg'oTE : — Crystalline and organic species Pp. 278 — 291 



CHAPTER XXIII. 



THE CAUSES OF DEVELOPMENT. 



How has the transmutation of species been caused '!— How has organic structure 

 been produced ? — We must begin by trj'ing known causes— Organization is 

 adaptation, morphological and histological— The problem twofold — The problem 

 stated — Two possible processes : self- adaptation, and natural selection— I believe 

 in an organizing Intelligence, over and above these, distinct from physical 

 causation — Where life i.s, there is intelligence : and most discernible in the 



