The Nematoda which are parasitic during their whole life may similarly be divided into two classes - those which undergo their development in a single host, and those which undergo their development in the bodies of two distinct hosts.
The soil to the depth of many feet, and from it springs the most marvellous tangle of huge trees, shrubs, bushes, underwood, creepers, climbing plants and trailing vines, the whole hung with ferns, mosses, and parasitic growths, and bound together by rattans and huge rope-like trailers.
The Nematode parasites of the Invertebrata are usually immature forms which attain their full development in the body of some vertebrate; but there are a number of species which in the sexually adult condition are peculiar to the Invertebrata.2 The Nematoda contain about as many parasitic species as all the other groups of internal parasites taken together; they are found in almost all the organs of the body, and by their presence, especially when encysted in the tissues and during their migration from one part of the body to another, give rise to various pathological conditions.
The parasitic and free-living Nematodes are connected by transitional forms which are free at one stage of their existence and parasitic at another; they may be divided into two classes those that are parasitic in the larval state but free when adult, and those that are free in the larval state but parasitic when adult.
Oxyuris, though chiefly parasitic in the Mammalia, occurs also in reptiles, Amphibia and one or two insects.
Although several species belonging to the second class occasionally enter the bodies of water snails and other animals before reaching their definitive host, they undergo no alteration of form in this intermediate host; the case is different, however, in Filaria medinensis and other forms, in which a free larval is followed by a parasitic existence in two distinct hosts, all the changes being accompanied by a metamorphosis.
Filaria medinensis - the Guinea worm - is parasitic in the subcutaneous connective tissue of man (occasionally also in the horse).
The members of this group are always carnivorous or parasitic, and prey upon both vertebrates and invertebrates.
In relation to their parasitic habit one or two suckers are always developed, the one at the anterior and the other at the posterior end of the body.
The marginal tentacles are rarely absent in non-parasitic forms, and are typically four in number, corresponding to the four perradii marked by the radial canals.
Polypodium hydriforme Ussow is a fresh-water form parasitic on the eggs of the sterlet.
The hydroid genus Lafoea is remarkable for producing gonothecae on the hydrorhiza, each containing a blastostyle which bears a single gonophore; this portion of the colony was formerly regarded as an independent parasitic hydroid, and was named Coppinia.
It is in these parasitic forms that we meet with the method of reproduction by sporogony described above.
The gametophyte, which bears the sexual organs, is either a free-living thallus corresponding in degree of differentiation with the lower liverworts, or it is a mass of cells which always remains enclosed in a spore and is parasitic upon the sporophyte.
It was not till De Bary (1866) made known the true nature of parasitic Fungi, based on his researches between 1853-1863, that the vast domain of epidemic diseases of plants was opened up to fruitful investigation, and such modern treatises as those of Frank (1880 and L895), Sorauer (1886), Kirchner (1890), were gradually made possible.
Parasitic Fungisupervening on its nonresistant condition.
Parasitic Fungi may be, as regards their direct action, purely locale.g.
Th~ phenomenon of irritability here concerned is well shown in certain cases where a parasitic organism gains access to a celle.g.
Still further insight is afforded by our increasing knowledge of the enzymes, and it is to be remarked that both poisons and enzymes are very common in just such parasitic Fungi as induce discolorations, hypertrophies and the death of cellse.g.
Those on turnips and other Cruciferae are due to the infection of Plasmodiophora, a dangerously parasitic Myxomycete.
In the American Epicauta vittata the larva is parasitic on the eggs and eggcases of a locust.
- Much difference of opinion has prevailed with regard to the curious, tiny, parasitic insects included in this division, some authorities considering that they should be referred to a distinct order, while others would group them in the family Meloidae just described.
The female is a segmented, wormlike creature, spending her whole life within the body of the bee, wasp or bug on which she is parasitic. One end of her body protrudes from between two of the abdominal segments of the host; it has been a subject of dispute whether this protruded end is the head or the tail, but there can be little doubt that it is the latter.
The chief points in the life-history of Stylops and Xenos, which are parasitic on certain bees (Andrena) and wasps (Polistes), have been investigated by K.
The growth of the parasitic larva does not stop the development of the host-larva, and when the latter pupates and assumes the winged form, the stylopid, which has completed its transformation, is carried to the outer world.
These and other experiments, described by Dr Manson in the Practitioner for March 1900, confirming the laboratory evidence as they do, leave no doubt whatever of the correctness of the mosquito-parasitic theory of malaria.
With regard to the parasites, which are the actual cause of malaria in man, an account of them is given under the heading of Parasitic Diseases, and little need be said about them here.
Short of suppressing mosquitoes, the parasitic cycle may theoretically be broken by preventing them from giving the infection to man or taking it from him.
The parasitic cycle has been broken, and the insect is no longer infected.
Certain extremely aberrant Diptera, which, in consequence of the adoption of a parasitic mode of life, have undergone great structural modification, are further remarkable for their peculiar mode of reproduction, on account of which the families composing the group are often termed Pupipara.
Pear scab is caused by a parasitic fungus, Fusicladium pyrinum, very closely allied and perhaps merely a form of the apple scab fungus, F.
W, The parasitic hydromedusa Mnestra, usually found attached in this position by the aboral pole of its umbrella.
Thyca, parasitic on asterids.
Entocolax, mouth at free extremity, animal fixed by aboral orifice of pseudopallium, Pacific. Entoconcha, body elongated and tubular, animal fixed by the oral extremity, protandric hermaphrodite, parasitic in testes of Holothurians causing their abortion.
Many of the adults are bloodsuckers (Tabanidae, Culicidae, &c.); others are parasitic in their larval stage (Oestridae, &c.).
In modern countries it takes myriads of forms, from the sweating of parasitic trades to the organization of scientific research.
Other genera of the family are parasitic on Hemiptera - bugs and frog-hoppers - but nothing is known as to the details of their life-history.
The yellowing and subsequent casting of leaves, for instance, is a very general symptom of disease in plants, and may be induced by drought, extremes of temperature, insufficient or excessive illumination, excess of water at the roots, the action of parasitic Fungi, insects, worms, &c., or of poisonous gases, and so forth; and extreme caution is necessary in.
Its over-supply is, however, a frequent cause of predisposition to the attacks of parasitic Fungie.g.
In these species the actinula is parasitic upon another medusa; for instance, Cunoctantha octonaria upon Turritopsis, C. proboscidea upon Liriope or Geryonia.
The parasitic actinula is found attached to the proboscis of the medusa; it thrusts its greatly elongated hypostome into the mouth of the medusa and nourishes itself upon the food in the digestive cavity of its host.
With the exception of these forms, reduced for the most part in correlation with a semi-parasitic mode of life, the tentacles are usually numerous.