Differentiation within the vertebrate phylum is therefore not uniserial, but takes place in several directions.
The archetype of the genus, family, order, class and phylum was thus conceived to have had at some past time a real existence.
Lamarck's term Annelides, now used to denote a major phylum or division of coelomate invertebrate animals.
The hard calcareous substance to which the name coral is applied is the supporting skeleton of certain members of the Anthozoa, one of the classes of the phylum Coelentera.
The relationships of the Arthropoda thus stated are shown in the subjoined table:-- / Sub-phylum 1.
The characters of the sub-phylum and those of the associated sub-phyla Chaetopoda and Rotifera have been given above, as well as the general characters of the phylum Appendiculata which comprises these great sub-phyla.
Further, in all members of the sub-phylum Chaetopoda the relative position of the prostomium, mouth and peristomium or first ring of the body, retains its primitive character.
The phylum of Worms, on the other hand, we have to conceive as a low bush or shrub, out of whose root a mass of independent branches shoot up in different directions.
Defn: A phylum of the vegetable kingdom consisting of the class Myxomycetes.
Defn: A phylum of plants of very diverse habit and structure, including the algæ, fungi, and lichens.
For this reason the terms Anthrophyta, Phænogamia, and Panerogamia have been superseded as names of the phylum by Spermatophyta.
Defn: A phylum embracing the highest plants, or those that produce seeds; the seed plants, or flowering plants.
By those who do not separate the Myxophyta from the Tallophyta as a distinct phylum the latter is treated as the lowermost group in the vegetable kingdom.
The phylum Nematothelminthes contains an assemblage of related worms, some marine, but mostly living in fresh waters or on land, which are eellike in form, very slender, and often have amazing length.
The critical point in the history of this phylum is passed when its members migrated from water to the land.
These are moss animals, representing the class Polyzoa of the phylum Molluscoida.
The universal occurrence of this structure has been regarded as the most important characteristic of the Vertebrata and their allies, which are accordingly grouped together in the phylum Chordata.
This definition requires the inclusion of various creatures very unlike "vertebrates," and the phylum therefore embraces three subdivisions: 1.
There can be but little doubt that the eye of the Tunicata belongs to the same phylum as that of the true Vertebrata, different as the two eyes are.
At the same time there appear to be strong arguments for regarding the Porifera as a phylum of the Metazoa derived independently from the Protozoa.
The bilateral symmetry of Chiton, which is quite as well marked as that of the Lamellibranchiata, indicates that it is a primitive phylum of the Odontophora.
In the face of what is known of their development it is hardly credible that they can represent a degenerate Chaetopod phylum in which segmentation has become lost.
The somewhat unexpected conclusion that the Arthropoda have a double phylumis on the whole borne out by the anatomy of the two groups.
On the other hand, the presence of chelate appendages innervated in the adult by the supra-oesophageal ganglia rather points to a common phylum for the Pycnogonida and Arachnida; though as shewn above (p.
The Cirripedia are believed by Claus to belong to the same phylum as the Copepoda.
What applies to the vertebrate phylum applies also to the invertebrate groups.
What evidence is there as to the origin of the bony skeleton in the vertebrate phylum itself?
As to the auditory apparatus itself, we see that the elaborate organ for hearing--the cochlea--has been evolved in the vertebrate phylum itself.
The group or Phylum Protozoa is divided into four smaller groups or classes.
The phylum Porifera or Spongiae includes the simplest of the Metazoa or multicellular animals.
An example of widely divergent groups within the same phylum has already been shown in the /Echinodermata/.
Each phylumis composed of a group of animals with a plan of structure which is common to themselves, but differs from that of the animals of all other phyla.
Next to the /Gasteropoda/, it is the largest class of the phylum in number of genera and species.
Little by little thephylum has been shorn of orders and classes.
As accepted by zooelogists to-day, this phylum is but the remnant of its former self.
The phylum also includes, as one of its large suborders, all the snails and slugs that are to be found crawling upon the land.
They are reactions which have long proved advantageous to the phylum of which the existent animal is the representative embodiment.
