502 



SCIENCE 



[N. S. Vol. XXVI. No. 668 



classifications of the nature-philosophers, 

 physiophilosophers, circularians, quinari- 

 ans, trinitarians, septenarians, and their 

 like that fiourished during the first half 

 of the past century. 



DEVELOPMENT THEOBT 



Although there had been previous indi- 

 cations of belief that transmutation of spe- 

 cies might have been a cause for the di- 

 versity of animal life, Jean Baptiste Pierre 

 Antoine de Monet de Lamarck (1809) first 

 framed a hypothesis that had a logical 

 basis, although weakened by unproved pos- 

 tulates. In view of those weaknesses, it 

 was easy to bring forth many facts that 

 seemed to militate unanswerably against 

 it, and such were well put forward by 

 Cuvier; as the hypothesis, too, was very 

 unpopular, it was for a long time stifled. 

 In the meanwhile geological and paleonto- 

 logical investigation, comparative morphol- 

 ogy, physiology and embryology, as well as 

 systematic zoology, were revealing innu- 

 merable facts that pointed all in the same 

 direction and were only explicable collect- 

 ively by the assumption that they were the 

 result of original community of origin and 

 subsequent deviation by gradual changes 

 from time to time. The facts were at 

 length collocated with extreme skill by 

 Charles Darwin (1859) and a rational ex- 

 planation of their evolution by means of 

 natural selection made the new develop- 

 ment theory acceptable to well-informed 

 naturalists and logical thinkers generally. 



SEQUENCE OF GROUPS 



It had been almost the universal custom 

 from olden time, as well as during the Lin- 

 nsean era, to commence the enumeration 

 - or catalogues of animals with the forms 

 exhibiting most analogy with man and 

 consequently the highest in the scale of 

 organic nature. As long as species were 

 assumed to be individually created this was 



perhaps the most natural course, and at 

 least had the advantage of proceeding from 

 the comparatively known to the almost un- 

 known. A significant and noteworthy ex- 

 ception to this mode of procedure among 

 the old naturalists was afiiorded by La- 

 marck (1809 et seq.), the precursor in this 

 respect as well as in recognition of descent, 

 of the modern school. 



When it became generally recognized 

 that there had been always a progression 

 and development from antecedent forms, 

 naturally there was a change in the man- 

 ner of exposition of a series, and the lowest 

 forms were taken as the initial ones and 

 followed by those successively higher in the 

 scale of beings. Even when old prejudices 

 were administered to and the highest ani- 

 mals put first in a work, it was often done 

 in a reversed series; that is, after the sup- 

 posed natural ascensive series had been de- 

 termined on, that series was simply re- 

 versed in order that the highest should be 

 the first and the lowest the last. Many of 

 our text-books of zoology still have this 

 characteristic, but are being rapidly re- 

 placed by those exhibiting the phyletic 

 series. 



HISTOLOGY 



One of the most noteworthy modifica- 

 tions of systematic zoology was the fruit 

 of histological research. In 1839 Theodor 

 Schwann, incited by the brilliant results 

 of Matthias Jacob Schleiden's researches 

 (1838) in vegetal histology, and at the 

 suggestion of Johannes Miiller, undertook 

 investigations which led him to consider 

 that the animal frame was built up from 

 innumerable cells variously modified to 

 form the diiierent systems and organs of 

 which it is composed. Ultimately the ani- 

 mals thus developed were segregated by 

 Ernst Haeckel, and the animal kingdom 

 was limited to them, while the simple uni- 

 cellular animals which had been already 

 designated as Protozoa were associated with 



