Nematode

“ There are also nematode worms which exist under these conditions, and which develop and propagate their species in the intestines as if in the midst of damp earth. The small eel-like creatures so abundant in cow-dung propagate in it; they are not parasites, and are allied to those of which we speak in this chapter.
Besides those attendants which busy themselves about the cleanliness of other animals, we find some whose duties are less extensive, and whose cares are more limited. ”

“ The demonstration of nematode-like formations in the vitreous remains uncertain even when movements are observed, and when they cannot be extracted and examined microscopically the doubt may occur that one may have mistaken the remains of the hyaloid artery for a worm, which it resembles in form, size and colour; the slightest movement of the eye also causes it to move so that it simulates a living organism. ”

“ If any argument were necessary to show how desirable it is to furnish full descriptions of the commoner kinds of parasite, I could adduce numerous instances that have been brought under my notice where professional men and others have been entirely mistaken as to the essential nature of their parasitic finds. Thus, I have known an instance where a great authority on the diseases of dogs has persisted in asserting for the free proglottides of a tapeworm a nematode origin; and, in like manner, human tapeworm-segments have frequently been mistaken for independent fluke parasites. ”

“ Deep-sea cold seeps and hydrothermal vents are both characterized by low nematode diversity and high dominance of single species. The low genera and species richness can be explained by the harsh physico-chemical conditions present in both ecosystems. There is no unique affinity with seeps or vents at genus level, suggesting a lower taxonomic level of endemicity for nematodes compared with mega- and macrofauna. Dominant nematode genera varied among the different seeps and hydrothermal vents. ”

“ Sixty millions of eggs have been counted in a single nematode, and in a single tape-worm, or rather in a colony, even a thousand millions of eggs. Even the very animals which live as parasites, harbour others in their turn. We find parasites on parasites, as we find messmates upon messmates. ”

“ Some are to be met with in all the organs—the brain, the eye, the muscles, the heart, the lungs, the tracheal artery, the frontal sinus, the digestive tube, the skin, and even in the blood. Sometimes the two sexes live under the same conditions; sometimes the male is dependent on its female, or else one generation is parasitical, and the next is independent. There is a great diversity with respect to development. Some nematodes, like trichinæ, are developed so rapidly, that the embryos are already perfect in the egg before it has quitted its mother. ”

“ Practically all roots are attacked by some kind of nematode, but many species appear to specialize on one type of plant and will not touch a different variety, even if no other food is available. Plants immune to one species may be highly susceptible to some other. A few kinds of these worms, however, appear to eat almost anything they can find underground. ”

“ History.— Our knowledge of this subject dates from the discovery by Demarquay, in 1863, of a larval nematode— microfilaria bancrofti (Plate X.) —in the milky fluid from a case of chylous dropsy of the tunica vaginalis. Later, in 1866, Wiicherer found the same organism in the urine of a number of cases of chyluria. In 1870 Lewis made a similar observation in India, and in 1872 discovered that the blood of man was the normal habitat of this larval parasite, which he named, accordingly, Filaria sanguinis hominis. ”

“ The whole body structure of the plant nematode is almost ideally suited to life in the soil. The typical eel-shaped body is well-adapted for moving in the moisture surrounding soil particles. Deviations from this eel-form in certain stages of some species, usually in mature females, are found only in sedentary stages. The larvae and males retain the ancestral shapes. Another deviation is found in the so-called “ring nematodes” which have short, plump bodies incapable of locomotion in the typical whip-like fashion. Movement is accomplished by alternate expansion and contraction of the body. ”

“ Another common nematode, the Oxyurus vermicularis (Fig. 69) , a parasite of man, is a small worm of the size of a fine pin, which often multiplies in the rectum of children, causing intolerable itching. It is by means of their microscopic eggs that they penetrate into the system; these are hatched in the stomach, and are completely developed at the end of eight or ten days. They pass from the anus in great numbers.
Fig. 68.—Trichocephalus of man.—1, female, a, cephalic extremity, b, caudal extremity and anus, c, d, digestive tube and ovary, e, orifice of sexual apparatus. ”

“ However, also the presence of other benthic taxa may interfer with the nematode success. In addition to nematodes, polychaetes of sulphide tolerant families, such as Capitellidae, Spionidae and Dorvilleidae, may thrive in the same seep conditions [4] , and may compete with them for food, space or oxygen, or act as potential predators. Two studies indicate a significant negative correlation between meio- and macrofauna densities in sulphidic sediments from a whale fall [22] or at the seeps along the Nordic margin [41] .
Increased standing stock is not only explained by increased densities. ”

“ In contrast to seeps, deep-water hydrothermal vents in general do not show high nematode densities or biomass. The communities are often impoverished or show similar densities compared to their adjacent background habitats [20] – [30] , [21] (Table 1 and 3) . In bacterial mats 1–78 ind. 10 cm−2 [27] occurred, and on bivalves also only 1 to 72 ind.10 cm−2 were found [20] , [52] , [53] , [30] . The tube worm habitat showed a high variation from very low nematode densities (1 ind. 10 cm−2) to higher values of about 900 ind. ”

“ Minute Nematodes abound in moist soil, around the roots of plants, etc., and may easily be detected with the aid of a lens wriggling about amongst the particles of sand and earth. Of the animal parasites perhaps the most familiar is the "round worm" (Ascaris lumbricoides, Figs. 66 and 67) , which inhabits the alimentary canal of man; others are common in domesticated animals, as A. mystax in the cat and dog, and A. megalocephala in the horse and ox. They are also found living parasitically in plants (Fig. 77) , causing the formation of galls and other pathological growths ”

“ At vents, nematode densities and biomass are always low. It is likely that the presence of hard or soft substrates, the latter being more favourable for nematodes, is reponsible for the differential response between seeps and vents. Competition for food- or space with macro- or megafauna, or even the meiofauna such as copepods is possibly an additional factor responsible for the high variation at seeps and the lower numbers at vents, although evidence is lacking so far. ”

“ Eustrongylus gigas, Diesing.—This is by far the largest nematode known to science, the male sometimes measuring a foot in length and the female more than three feet, whilst the breadth of the body reaches half an inch at the thickest part. Though fortunately very rare in man, this worm is known to occur in a great variety of animals, especially in weasels. According to Weinland and Jackson, it is particularly abundant in the kidney of the North American mink (Mustela vison) , destroying the substance of the organ, the walls of which become the seat of calcareous deposit. ”

“ Nematode worms and their eggs were found by Uzel in the body-cavity. He found no less than 200 Nematodes in one Thrips, and noticed that they had entirely destroyed the ovaries. Woodpeckers, according to him, tear off the bark of trees and eat the Thysanoptera that are concealed thereunder, though one would have surmised that these minute Insects are too small to be game for such birds. They have, it appears, no special protection, except that one species (a larva of Phloeothrips sp.) is said to emit a protective fluid. ”

“ The Heteroura androphora is another nematode which lives in the stomach of tritons. The male is always rolled round the body of its female. The two sexes are always free, contrary to that which is observed in the syngami. The Blattæ, coleopterous insects, also harbour sexual nematodes. Radkewisch saw two species of anguillulæ, the Anguillula macroura and appendiculata, in the Blatta orientalis, and an Oxyuris brachyura in the Blatta germanica. These eggs leave the body with the feces, and resist the action of deleterious agents. ”

“ It would seem, in short, that the eggs of nematodes which normally take up their residence in cats, dogs, and in the carnivora which reside in arid regions, will develop embryos in the egg without external moisture. As before remarked, Davaine thinks it is not necessary that these nematode embryos should pass through any intermediary bearer, and he believes that they are often directly transferred to the stomach of their “hosts” whilst adhering in the form of an impalpable dust to the coats of their bearers, whence they are detached by the animal’s frequent habit of licking the fur. ”

“ Three possible reasons for the low nematode densities at vents are put forward: (1) The substrate is unsuitable for supporting high abundances. Vents consist of recently formed hard substrates, such as basalt or sulphide minerals precipitates, with no or little sediment covering the hard substrate. Vent fluid reaches the water column through sulphide chimneys or crack and crevices of basalt, on which large foundation species, such as bivalves and tubeworms, grow. Most hydrothermal vents provide living space for meiofauna only on these hard substrates, or on the associated foundation species. ”

“ The guinea-worm may be described as a nematode measuring from one to six feet in length, having a thickness of 1/10th of an inch. The body is uniformly cylindrical, terminating below in a more or less curved and mucronately pointed tail. The head is flatly convex or truncate, having a central, simple mouth, which is surrounded by four equi-distantly and cruciately disposed papillæ. The mode of reproduction is viviparous, the body enclosing a prodigious number of hatched embryos, which, by distension of the uterine ducts, almost entirely obliterate the somatic cavity. ”

“ Neither the temperament nor the humours have any influence on parasites, and they are not more abundant in delicate individuals than in those who enjoy the most robust health. On the contrary, all wild animals harbour their parasitical worms, and the greater part of them have not lived long in captivity, before nematode and cestode worms completely disappear. It is only the imprisoned parasites which do not desert them. ”

“ According to Davaine, the eggs of many nematode species will readily retain their vitality though long exposed to dryness, but their yolk-contents will not go on developing during this period of exposure. ”

“ There is scarcely a stage which may not be parasitic; the eggs, the larvae, the adults are all in some cases free, in others parasitic, and in many cases first the one and then the other.
2. Occurrence and Effect of the Parasite on the Host.—Von Linstow states that the only law that can be derived inductively from the study of the life-history of Nematodes is that those that live in animals never pass through all their stages of development in the same organ; consequently, in considering the distribution of {163}the parasites within the body of their host we have a double habitat to consider. ”

“ This apparently different physical nature of both chemosynthetic ecosystems is therefore likely to explain lower genera richness at vents. Other possible reasons are that the coexistence of nematodes, with various other, highly abundant epifaunal organisms at vents, might result in competitive exclusion, and could explain low eveness of single nematode species, in association with low densities. ”

“ In addition to the organisms already considered there are others of larger size. The nematodes are almost visible to the unaided eye, most of them are free living and probably help in the disintegration of plant residues, though a few are parasitic on living plants and do much injury to clover, oats, and less frequently to onions, bulbs, and potatoes. Further, there are insects, myriapods and others, the effects of which in the soil are not fully known. ”

“ The free larvae live in the earth and make their way into the smaller rootlets; here the female larvae shed their skin, lose their characteristic Nematode form, and become citron-shaped (Fig. 78, D) . The male larvae undergo a change, and after a period of rest cast their skin and, leaving the rootlet, seek out the females. The female does not undergo this second ecdysis, but its generative organs grow and mature in what is practically a larval stage. ”

“ In many forms the young stages live free for some time (Strongylidæ) , in others, as is the case in Rhabdonema, parasitic and free-living generations alternate; in others, again, the free period is limited to the egg stage or entirely suppressed.
Though it is possible thus to connect the parasitic with the free-living nematodes, by taking their manner of life into account, this matter presents greater difficulties in regard to other helminthes. ”

“ However the exact mechanisms of adaptation of Terschellingia or Sabatieria species to the sulphidic or oxic environment remains unclear. Some authors pointed to the presence of dark, often multilayered intracellular globules in the intestinal cells of nematode species typical for sulphidic muds (i.e. Sabatieria wieseri, Terschellingia longicaudata, Sphaerolaimus papillatus, Siphonolaimus ewensis, Pontonema vulgare) . ”

“ The Leptodera appendiculata inhabits the foot of the Arion empiricorum, in the larva state, and becomes sexual (male and female) in the decomposed body of the snail. The next generation has the sexes united, and lives in damp earth. The Leptodera pellio lives in the same way in the bodies of lumbrici; another Leptodera inhabits the intestine of the snail, and a third the salivary glands. The nematode so generally known under the name of Ascaris nigro-venosa also belongs to this genus. It lives in the lungs of the frog. ”