Head is the term applied to the anterior part of the body of an animal when marked off by a difference in size, or by a constriction (neck). A gradual increase of complexity in the structure of the head is observable as we ascend from the lowest to the highest forms of life. In the Protozoa, Infusoria, and Coelenterates nothing that can be regarded as a head is found, and it is not until we ascend to the worms proper, the articulated animals (crustaceans, myriapods, spiders, and insects), the land and fresh-water gasteropods (snails and whelks), and the cuttle-fishes, that a head proper is found.
The cuttle-fishes have a remarkable cartilaginous box, which, like a skull, protects their anterior nervous ganglia and gives support to the muscles. The head of the vertebrated animals presents a regular series of increasing complexity from the lancelet upwards, and as the anterior nervous mass enlarges, and its ganglia increase in complexity, so do the anterior vertebra change their character; as the brain becomes specialized, so does the brain-case or skull, attaining its highest development in man.
In man, and in the higher vertebrates, the head consists of an upper chamber, lodging the brain, the eyes, and other sense organs, and a lower, lodging the first portion of the alimentarycanal. In proportion as the vertebrates become developed, the brain increases in size, and its position advances anteriorly, until, in man, it comes to overhang the face.
Head is the unit of measurement of cattle. Thus a herd of 100 cattle is referred to as 100 head.
Balantidium is a Phylum Protozoa, a member of the order of Heterotricha.
Balantidium coli occurs in the cecum of swine, where it does no harm. However, on being transmitted to primates it can cause acute and even hemorrhagic diarrhoea and ulceration of the gut wall. Research Balantidium
Ciliata are a highly organised class of the Protozoa, characterised by the possession of cilia, which may be distributed all over the body, and act as swimming organs, as in the slipperanimalcule, or may be restricted to certain parts of it, as in the stalked bell animalcule, in which their action serves to sweep food-particles into the gullet. Research Ciliata
Ciliophora are a class of Protozoa with relatively simple life-histories. The locomotor structures are cilia arranged in definite tracts. The cilia arise from grooves in the pellicle. Ciliophora have a unique nuclear structure, comprised of a meganucleus concerned with trophic activities, and a micronucleus concerned with reproduction. Research Ciliophora
Foraminifera is an order of animals of low type belonging to the class Rhizopoda, of the Phylum Protozoa, furnished with a shell or test, simple or complex, usually perforated by pores called foramina from which the animals get their name.
The shell may be composed of horny matter, or of carbonate of lime, secreted from the water in which they live. Owing to the resemblance of their convoluted chambered shells to those of the nautilus, they were at first reckoned among the most highly organized molluscs. In reality they are among the simplest of the protozoa. The body of the animal is composed of granular, gelatinous, highly elastic sarcode, which not only fills the shell, but passes through the perforations to the exterior, there giving off long thread - like processes called pseudopodia interlacing each other so as to form a net like a spider's web. Internally the sarcode-body exhibits no structure or definite organs of any kind.
Foraminifera appear very early in the geological formations. The great formation known as white chalk is largely composed of foraminiferous shells, while another remarkable formation known as Nummulitic Limestone receives its name from the presence of coin-shaped foraminifera, generally about 25 mm diameter. Research Foraminifera
Gregarinidae are a class of minute animal organisms comprising the lowest forms of Protozoa found parasitic in various animals, especially the cockroach and earthworm. The Gregarinidae consist of an outer colourless transparentmembrane, with only faint signs of a fibrillose structure inclosing a granular mass in which there is a nucleus surrounded by a clear space. Research Gregarinidae
The mastigophora (Flagellata) are a class of Phylum Protozoa. They are small Protozoa which are motile in the adult stage, swimming by means of flagella. They reproduce by logitudinal fission. Research Mastigophora
Abbreviations
Research Acrita
