Artwork by Alex Schomburg for Trouble on Titan A Winston Science Fiction novel. Introduction Once your rocket has landed on an alien planet, you need some transportation to get you around. In the Andre Norton and A.
The suborders Spirurina and Tylenchina and the infraorders RhabditomorphaPanagrolaimomorphaand Tylenchomorpha are paraphytic.
The monophyly of the Ascaridomorph is uncertain. Anatomy[ edit ] Internal anatomy of a male C. The mouth has either three or six lips, which often bear a series of teeth on their inner edges. The cuticle is often of complex structure, and may have two or three distinct layers.
Underneath the epidermis lies a layer of longitudinal muscle cells. The relatively rigid cuticle works with the muscles to Excretory system project a hydroskeleton, as nematodes lack circumferential muscles.
Projections run from the inner surface of muscle cells towards the nerve cords ; this is a unique arrangement in the animal kingdom, in which nerve cells normally extend fibres into the muscles rather than vice versa. The mouth often includes a sharp styletwhich the animal can thrust into its prey.
In some species, the stylet is hollow, and can be used to suck liquids from plants or animals. Digestive glands are found in this region of the gut, producing enzymes that start to break down the food. In stylet-bearing species, these may even be injected into the prey. This produces further enzymes, and also absorbs nutrients through its single-cell-thick lining.
The last portion of the intestine is lined by cuticle, forming a rectumwhich expels waste through the anus just below and in front of the tip of the tail. Movement of food through the digestive system is the result of body movements of the worm.
The intestine has valves or sphincters at either end to help control the movement of food through the body. However, the structures for excreting salt to maintain osmoregulation are typically more complex.
In most other nematodes, these specialised cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct.
This transverse duct opens into a common canal that runs to the excretory pore. Muscle arms Four peripheral nerves run the length of the body on the dorsal, ventral, and lateral surfaces. Each nerve lies within a cord of connective tissue lying beneath the cuticle and between the muscle cells.
The ventral nerve is the largest, and has a double structure forward of the excretory pore. The dorsal nerve is responsible for motor control, while the lateral nerves are sensory, and the ventral combines both functions.
Smaller nerves run forward from the ring to supply the sensory organs of the head. These are well supplied with nerve cells, and are probably chemoreception organs. A few aquatic nematodes possess what appear to be pigmented eye-spots, but whether or not these are actually sensory in nature is unclear.
Both sexes possess one or two tubular gonads. In males, the sperm are produced at the end of the gonad and migrate along its length as they mature.
The testis opens into a relatively wide seminal vesicle and then during intercourse into a glandular and muscular ejaculatory duct associated with the vas deferens and cloaca.
In females, the ovaries each open into an oviduct in hermaphrodites, the eggs enter a spermatheca first and then a glandular uterus. Males are usually smaller than females or hermaphrodites often much smaller and often have a characteristically bent or fan-shaped tail.
During copulationone or more chitinized spicules move out of the cloaca and are inserted into the genital pore of the female. Amoeboid sperm crawl along the spicule into the female worm.
Nematode sperm is thought to be the only eukaryotic cell without the globular protein G-actin. Eggs may be embryonated or unembryonated when passed by the female, meaning their fertilized eggs may not yet be developed.
A few species are known to be ovoviviparous. The eggs are protected by an outer shell, secreted by the uterus. In free-living roundworms, the eggs hatch into larvaewhich appear essentially identical to the adults, except for an underdeveloped reproductive system; in parasitic roundworms, the lifecycle is often much more complicated.
The juvenile nematodes then ingest the parent nematode. This process is significantly promoted in environments with a low food supply.Four peripheral nerves run the length of the body on the dorsal, ventral, and lateral surfaces. Each nerve lies within a cord of connective tissue lying beneath the cuticle and between the muscle cells.
The ventral nerve is the largest, and has a double structure forward of the excretory schwenkreis.com dorsal nerve is responsible for motor control, while the lateral nerves are sensory, and the. Renal system, in humans, organ system that includes the kidneys, where urine is produced, and the ureters, bladder, and urethra for the passage, storage, and voiding of urine..
In many respects the human excretory, or urinary, system resembles those of other mammalian species, but it has its own unique structural and functional . A cephalopod (/ ˈ s ɛ f ə l ə p ɒ d, ˈ k ɛ f-/) is any member of the molluscan class Cephalopoda (Greek plural κεφαλόποδα, kephalópoda; "head-feet") such as a squid, octopus or schwenkreis.com exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot.
This award-winning interactive program is part of the "Whole Frog" schwenkreis.com can interactively dissect a (digitized) frog named Fluffy, and play the Virtual Frog Builder Game. The interactive Web pages are available in a number of languages.
Click on the frog to dive into the kit. Help and additional information available include a tutorial, an overview of how the system works, a paper that. A Kid's Guide to Life Sciences: The Human Body Systems. Human anatomy is the study of the systems of the body which is made up of cells, tissues, and organs.
A Skeptical Look at the Spooky2 Rife System Jay Frost. Spooky2 is an array of devices based on the theories of Royal Raymond Rife (), an American inventor.