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Grasshopper

Introduction to phylum

Grasshoppers are members of the largest phylum, Arthropoda. The phylum Arthropoda contains over one million identified species. All arthropods feature jointed legs and exoskeletons. Exoskeletons are structures made up of chitin and protein which protect and give shape to their owners, as well as holding the internal organs in place. Unlike regular skeletons, however, exoskeletons must be shed and regrown as the arthropod develops.

All arthropods also feature antennae. These are special appendages which are used for a variety of tasks, including feeling, smelling, feeding and mating. Like the annelids (including the earthworm), arthropods feature segmentation. In the grasshopper, this allows for maneuverability. Grasshoppers have eleven segments; however, some arthropods may have as many as 400.

Digestion and excretion

The digestive system of insects includes a foregut (stomodaeum - the mouth region), a hindgut (proctodaeum - the anal region), and a midgut (mesenteron). The mouth leads to the muscular pharynx (which sucks and swallows), and through the esophagus to the crop. This discharges into the midgut, which leads to the malpighian tubules. These are the chief excretion organs. The hindgut includes intestine parts (including the ileum and rectum), and exits through the anus. Most food is handled in the midgut, but some food residue as well as waste products from the malpighian tubules are managed in the hindgut. These waste products consist mainly of uric acid, urea and a bit of amino acids, and are normally converted into dry pellets before being disposed of.

The salivary glands and midgut secrete digestive enzymes. The midgut secretes protease, lipase, amylase, and invertase, among other enzymes. The particular ones secreted vary with diet.

Nervous System

The grasshopper's nervous system is controlled by ganglia, dense groups of nerve cells which are found in most animals more advanced than cnidarians. In grasshoppers, there are ganglia in each segment as well as a larger set in the head, which are considered the brain. There is also a neuropile in the centre where all of the ganglia channel signals through. The sense organs (sensory neurons) are found near the exterior of the body and basically consist of tiny hairs (sensilla), made up of one sense cell and one nerve fibre, which are each specially calibrated to sense a certain thing. While the sensilla are found all over the body, they are most dense on the antennae, palps (part of the mouth), and cerci (near the posterior end). Grasshoppers also have tympanal organs for sound reception; both these and the sensilla are linked to the brain via the neuropile.

Reproduction

The grasshopper's reproductive systems consists of the gonads, the ducts which carry sexual products to the exterior, and accessory glands. In males,t he testes are made up of a number of follicles which hold the spermatocytes as they mature and form packets of elongated spermatozoa. After they are liberated in bundles, these spermatozoa accumulate in the vesicula seminalis (vas deferens).

In females, each ovary is made up of ovarioles. These converge upon the two oviducts, which unite to create a common oviduct which carries ripe eggs. Each of the ovarioles is made up of a germarium (a mass of cells that form oocytes, nurse cells, and follicular cells) and a series of follicles. The nurse cells nourish the oocytes during early growth stages, and the follicular cells provide materials for the yolk and make the eggshell (chorion).

During copulation, the male introduces sperm into the vagina through its aedeagus (reproductive organ). The sperm enters the eggs through fine canals called micropyles. The eggs are usually laid in soil, although they can also be laid in plant roots or even manure.

Circulation and respiration

Grasshoppers have open circulatory systems, with most of the body fluid (hemolymph) filling body cavities and appendages. The one closed organ. the dorsal vessel, extends from the head through the thorax to the hind end. It is a continuous tube with two regions - the heart, which is restricted to the abdomen, and the aorta, which extends from the heart to the head through the thorax. Hemolymph is pumped forward from the hind end and the sides of the body through a series of valved chambers, each of which contains a pair of lateral openings (ostia). The hemolymph continues to the aorta and is discharged through the front of the head. Accessory pumps carry hemolymph through the wings and along the legs and antennae before it flows back to the abdomen. This hemolymph circulates nutrients through the body and carries metabolic wastes to the malphighian tubes to be excreted. Because it does not carry oxygen, grasshopper "blood" is green.

Respiration is done through tracheae, air-filled tubes which open at the surfaces of the thorax and abdomen through pairs of spiracles. The spiracle valves only open to allow oxygen and carbon dioxide exchange. The tracheoles, found at the end of the tracheal tubes, are insinuated between cells and carry oxygen through the body.

Locomotion

Grasshoppers can walk, crawl and hop using their six legs. Their hind legs are very strong and can assist their wings (attached to the thorax) to allow leaps over very long distances (up to 20 times its body length). This allows them to escape predators and attack prey fairly easily.

Symmetry and special characteristics

Grasshoppers are bilaterally symmetrical. They feature compound eyes which provide a much higher quality of vision than those of humans, due to the higher resolutions of the mosaics created by the compound eyes.

Resources

"orthopteran." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 17 May 2005 <http://www.britannica.com/eb/article?tocId=9105957>.

"arthropod." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 17 May 2005 <http://www.britannica.com/eb/article?tocId=9117436>.

"insect." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 17 May 2005 <http://www.britannica.com/eb/article?tocId=9105953>.

"ganglion." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 17 May 2005 <http://www.britannica.com/eb/article?tocId=9035998>.

"Grasshopper." Wikipedia, the free encyclopedia. 11 May 2005, 21:41 UTC. 16 May 2005 <http://en.wikipedia.org/wiki/Grasshopper>.