In the arrangement of the separate sections, a classification according to contents was impracticable because of the variety of subjects often dealt with in one sura.
In his researches, Roscoe showed that the atomic weight of the metal as determined by Berzelius and the formulae given to the oxides were incorrect, and pointed out that the element falls into its natural place in group V of the periodic classification along with phosphorus and arsenic, and not in the chromium group where it had originally been placed.
It is impossible to enumerate or to give due consideration to all the names in the army of anatomical and embryological students of the middle third of the 19th century whose labours bore fruit in the modification of zoological theories and in the building up of a true classification of animals.
Huxley adopted in his lectures (1869) a classification which was in many respects similar to both of the foregoing, but embodied improvements of his own.
The former classification into Holochlamyda, Pneumochlamyda and Siphonochlamyda has been abandoned, as it was founded on adaptive characters not always indicative of true affinities.
A physiological classification according to an action on the brain, heart, kidney or other important organ becomes still more bewildering, as many substances produce the same effects by different agencies, as, for instance, the kidneys may be acted upon directly or through the circulation, while the heart may be affected either through its muscular substance or its nervous apparatus.
However, Nitzsch had not as yet seen his way to proposing any methodical arrangement of the various groups of birds, and it was not until some eighteen months later that a scheme of classification in the main anatomical was attempted.
Meanwhile the English naturalist, John Ray, was studying the classification of animals; he published, in 1705, his Methodus insectorum, in which the nature of the metamorphosis received due weight.
A statement may now be given of Gadow's classification of birds, in which the extinct forms have been intercalated so far as possible.
BERYLLIUM, or Glucinum (symbol Be, atomic weight 9.1), one of the metallic chemical elements, included in the same sub-group of the periodic classification as magnesium.