468 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
the old naturalists was afforded by Lamarck (1809 et seq.), the pre- 
cursor in this respect, as well as in recognition of descent, of the mod- 
ern 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 manner 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 admin- 
istered to and the highest animals put first in a work, it was often 
done in a reversed series; that is, after the supposed natural ascensive 
series had been determined on, that series was simply reversed 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 replaced by those exhibiting the phyletic series. 
HISTOLOGY. 
One of the most noteworthy modifications of systematic zoology 
was the fruit of histological research. In 1839 Theodor Schwann, 
incited by the brillant results of Matthias Jacob Schleiden’s re- 
searches (1838) in vegetal histology, and at the suggestion of Jo- 
hannes Miiller, undertook investigations which led him to consider 
that the animal frame was built up from innumerable cells variously 
modified to form the different systems and organs of which it is 
composed. Ultimately the animals thus developed were segregated 
by Ernst Haeckel, and the animal kingdom was limited to them, while 
the simple unicellular animals which had been already designated 
as Protozoa were associated with unicellular plants under the general 
term Protista. One of the prominent features of this idea was ac- 
cepted by Thomas Henry Huxley (1874) with, however, the very 
important modification of retaining the old conception, the animal 
kingdom, and keeping the name Protozoa as the collective name of 
the unicellular animals while taking a suggested name of Haeckel’s 
(Metazoa) for the multicellular animals. 
GRADUAL DELIMITATION OF GENERA. 
As has been already noted, the animal genera of Linné were mostly 
extremely comprehensive, answering, when natural groups, to fami- 
lies, superfamilies, and even orders or classes of modern naturalists. 
Such contrast, however, with others of the Linnean genera, and when 
this fact became recognized and it was discovered that the large 
genera embraced types exhibiting many differences in detail, the lat- 
ter were subdivided; early in the past century, at first owing espe- 
cially to French and German naturalists, the subdivision of old 
genera on approximately present lines was commenced and applied at 
