The reason for this extreme degeneration is probably to be found in the sandy nature of the soil in which the creature burrows, a substance which would evidently irritate and inflame any functional remnant of an eye.
The gonophores of different hydroids differ greatly in structure from one another, and form a series showing degeneration of the medusa-individual, which is gradually stripped, as it were, of its characteristic features of medusan organization and finally reduced to the simplest structure.
A very early stage in the degeneration is well exemplified by the so-called " meconidium " of Gonothyraea (fig.
Medusa-buds) in the extreme of degeneration, then it follows from Brooks's theory that Hydra must be descended from an archaic form in which the medusan type of organization had not yet been evolved.
Just as in the Mediterranean region, the degeneration of forests has given rise to mhquis and garigues, so in western Europe, the degeneration of forests has brought about different types ot grassland, heaths, and moors.
But, as will be pointed out later, organs are often found to have undergone degeneration or reduction, and such reduced or degenerate structures may easily be mistaken for primitive structures, and so the investigator may be misled.
A survey of the vegetable kingdom indicates that evolution has proceeded, on the whole, from the simple to the complex; at the same time, as has been already mentioned, evidence of reduction or degeneration in common.
The young pigeons are fed by both parents with a peculiar stuff, the product of the strongly proliferating epithelial cells of the crop, which cells undergo a cheese-like fatty degeneration, and mixed with mucus, perhaps also with the proventricular juice, make up a milklike fluid.
Degeneration of prayer: W.
As might be expected, degeneration in larval structure is correlated with a concealed habit of life.
But, excluded though they were from most trades and occupations, confined to special quarters of the city, disabled from sharing most of the amenities of life, the Jews nevertheless were gradually making their escape from the ghetto and from the moral degeneration which it had caused.
He found on both sides an unreadiness for approximation: the Jews had sunk into apathy and degeneration, the Christians were still moved by hereditary antipathy.
Despite all this, one must not fall into the easy error of exaggerating the degeneration into which the Jewries of the world fell from the middle of the 17th till the middle of the 18th century.
But in the other members of the sub-class the detorsion of the visceral mass has carried back the anus and circumanal complex from the anterior dorsal region to the right side, as in Bulla and Aplysia, or even to the posterior end of the body, as in Philine, Oncidium, Doris, &c. Different degrees of the same process of detorsion are, as we have seen, exhibited by the Heteropoda among the Streptoneura, and both in them and in the Euthyneura the detorsion is associated with degeneration of the shell.
The variety of special developments of structure accompanying the atrophy of typical organs in the Opisthobranchia and general degeneration of organization is very great.
Some Opisthobranchia are striking examples of degeneration (some Nudibranchia), having none of those regions or processes of the body developed which distinguish the archaic Mollusca from such flat-worms as the Dendrocoel Planarians.
It has, moreover, been noticed that even in cases where phagocytosis exists a greater or less extent of degeneration of the tissue may be observed before phagocytosis occurs.
And the evil effects of nervous degeneration find a more recent illustration in the mysticism of the Chasidim (Hdsidim, " saints "), a Jewish sect in eastern Europe which started from a movement in the 38th century against the exaggerated casuistry of contemporary rabbis, and combined much that was spiritual and beautiful with extreme emotionalism and degradation.
So, too, degeneration is not to be lightly assumed as the explanation of a simplicity of structure.
There is a very definite criterion of the simplicity due to degeneration, which can in most cases be applied.
Further: degeneration cannot be inferred safely by the examination of an isolated case; usually we obtain a series of forms indicating the steps of a change in structure - and what we have to decide is whether the movement has been from the simple to the more complex, or from the more complex to the simple.
Spencer), as in the Araneae and Opiliones, and, on the other hand, may terminate in simplification and degeneration, as in the Acari.
The reduction of the organism to seven leg-bearing somites, of which the first pair, as in so many Eu-arachnida, are chelate, is a form of degeneration connected with a peculiar quasi-parasitic habit resembling that of the crustacean Laemodipoda.
Idem, " Degeneration, a Chapter in Darwinism," 1878, reprinted in the Advancement of Science (Macmillan, 1890); 20.
Claus, " Degeneration of the Acari and Classification of Arthropoda," Anzeiger d.
Another important factor in the present condition of zoological knowledge as represented by classification is the doctrine of degeneration propounded by Anton Dohrn.
It is Dohrn's merit to have pointed out 1 that this assumption is not warranted, and that degeneration or progressive simplification of structure may have, and in many lines certainly has, taken place, as well as progressive elaboration and in other cases continuous maintenance of the status quo.
The general purpose is to give something like an equivalence of importance to divisions or branches indicated by the same term, but it is not intended to imply that every phylum has the Ursprung der Wirbelthiere (Leipzig, 1875); and Lankester, Degeneration (London, 1880),, ti, ae / .r ?
A knowledge of the bacteriology of scrofulous affections of bone and joints, such as caries and gelatinous degeneration, has shown that they also are tubercular diseases - that is to say, diseases due to the presence locally of the tubercle bacillus.
The muscles suffer at an early period: they fall off in bulk, and later suffer from fatty degeneration, the heart being probably the first muscle to give way.
The earliest interpretation put upon this experiment was that the trophic influence of the nerve having been withdrawn, the tissue failed to nourish itself, and that degeneration ensued as a consequence.
A salivary gland degenerates when its nerve-supply is cut off; and the nerves leading up to the symmetrical sloughs in Raynaud's disease have been found in an advanced state of degeneration (Affleck and Wiglesworth).
When a nerve-trunk is separated from its central connexion, the distal portion falls into a state of fatty degeneration (Wallerian or secondary degeneration).
The toxic actions produced in continued fevers, in certain chronic diseases, and by intestinal parasites largely aid in producing degeneration, emaciation and atrophy.
Thus workers in lead suffer from the effects of this substance as a poison, those who work in phosphorus are liable to necrosis of bone and fatty degeneration of the blood vessels and organs, and the many occupations in which dust is inhaled (coalmining, stone-dressing, steel-polishing, &c.; fig.
Cell in a state of degeneration and chromatolysis; the large rounded body in the cell is a cancer parasite.
- Fatty degeneration of heart from case of perni cious anaemia.
In many pathological conditions this tissue is commonly found to undergo mucoid or myxomatous degeneration, which is regarded as a reversion to a closely similar type - that of foetal connective tissue (fig.
This term is usually applied to a semi-solid substance of homogeneous and gelatinous consistence, which results partly from excretion and partly from degeneration of cellular structures, more particularly of the epithelial type.
Serous degeneration is met with in epithelial cells in inflammatory conditions and following on burns.
Fatty degeneration is a retrogressive change associated with the deposit of fatty granules or globules in the cytoplasm, and is caused by disorganized cellular activity (figs.
Over and above the bacterial intoxications we have a very extreme degree of fatty degeneration, widely distributed throughout the tissues, which is produced by certain organic and inorganic poisons; it is seen especially in phosphorus and chloroform poisoning.
Fatty degeneration is common to all dead or decaying tissues in the body, and may be followed by calcification.
Autolysis is a disintegration of dead tissues brought about by the action of their own ferments, while degeneration takes place in the still living cell.
From whatever cause the tissues become disorganized and undergo fatty degeneration, the fatty acids may become liberated and combine with the alkalies to form potash and soda soaps.
The fibrils of the outer coat also show the change to a less extent, while the degeneration very rarely spreads to the middle coat.
Hyaline degeneration is found in certain acute infective conditions; the toxins specially act on these connective-tissue cell elements.
They are probably a degeneration-product of cells.
611; Pelagatti, " Blastomycetes and Hyaline degeneration," Arch.
Waller (1816-1870), who tracked the line of nervous strands by experimental sections, and showed that when particular strands are cut off from their nutritive centres the consequent degeneration follows the line of the separated strands.