THE SEVEN MODERN TYPES. 121 
or Zoophyta)—the sponges, corals, hood-jellies, and comb- 
jellies. At the same time, Siebold united the Infusoria with 
the Rhizopoda, under the name of Protozoa (lowest animals), 
into a special main division of the animal kingdom. By 
this the number of animal types was increased to six. It 
was finally increased to seven by the fact that modern 
zoologists separated the main division of the articulated 
animals into two groups: (a) those possessing articulated 
feet (Arthropoda), corresponding to Linneus’ Insects, 
namely, the Flies (with six legs), Myriopods, Spiders, and 
Crustacea ; and (b) the footless Worms (Vermes), or those 
possessing non-articulated feet. These latter comprise only 
the real or genuine Worms (ring-worms, round worms, 
planarian worms, etc.), and therefore in no way correspond 
with the Worms of Linnzeus, who had included the molluscs, 
the radiates, and many other lower animals under this name. 
Thus, according to the views of modern zoologists, which 
are given in all recent manuals and treatises on zoology, 
the animal kingdom is composed of seven completely distinct 
main divisions or types, each of which is distinguished by a 
characteristic plan of structure peculiar to it, and perfectly 
distinct from every one of the others. In the natural system 
of the animal kingdom—which I shall now proceed to explain 
as its probable pedigree—I shall on the whole agree with 
this usual division, but not without some modifications, which 
I consider very important in connection with genealogy, 
and which are rendered absolutely necessary in consequence 
of our view as to the history of the development of animals. 
We evidently obtain the greatest amount of information 
concerning the pedigree of the animal kingdom (as well as 
concerning that of the vegetable kingdom) from comparative 
