DEGENERATION. This term is used in several ways in biology. It is applied by Sir E. Ray Lankester (189o) to a racial change in the direction of simplification, as contrasted with elabor ation or with persistent balance. An ascidian is in some respects degenerate, e.g., in its nervous system, as compared with its pre sumed free-swimming ancestor, or its actual free-swimming larva. Lankester defined degeneration as "a gradual change of structure in which the organism becomes adapted to less varied and less complex conditions of life; whilst elaboration is a gradual change of structure, in which the organism becomes adapted to more and more varied and complex conditions of existence. In elabor ation there is a new expression of form, corresponding to new perfection of work in the animal machine. In degeneration there is suppression of form, corresponding to the cessation of work." He referred to the vestiges of limbs in certain lizards, such as Seps and Bipcs, to parasitic crustaceans such as Sacculina and Lernaeocera, sedentary types like rock-barnacles and ascidians, endoparasitic animals such as some mites and Linguatulids. Lan kester was careful to point out that "simplicative evolution" may be illustrated in some of the structures of an organism, while "elaborative evolution" is seen in others. Thus the ascidian is not degenerate as regards its pharynx. Lankester excluded cases where there is simplification in the number of parts, yet special ization of what remains, as in the horse limb, where only the third digit is well developed. Anton Dohrn (1875) may be mentioned as another naturalist of distinction who has emphasized degener ation as one of the alternatives of evolutionary change.
In the second place the term is often applied to retrogressive changes in the normal development, which appear to be conditions of subsequent re-differentiation of a new, and, it may be, more complicated plan. This is well illustrated in the metamorphosis of Diptera, Hymenoptera, Coleoptera, and Lepidoptera, where in varying degrees there is a destruction of the larval organization, sometimes by means of phagocytes, and a reconstruction on a new plan, that of the imago, the change being mainly due to very active complexes of small cells, called imaginal discs or folds. This was well described by Kowalevsky and by Weismann for the body-wall and alimentary tract of Dipterous larva. Analogous processes occur in other kinds of metamorphosis, as in the pilidium larva of Nemertines and the pluteus larva of sea-urchins. The dis solution of the complex tail of the tadpole is familiar and obviously much more localized than the thorough-going retrogressive changes in the pupating maggot of a blue-bottle. In these degenerative processes many cells are actually destroyed, but when the develop ment is continued on new lines it must be supposed that certain cells return to an undifferentiated embryonic condition, and that new hereditary factors, previously inhibited, find liberating stim uli and developmental expression.
Here the term de-differentiation is useful and has been defined as the process by which specialized cells or tissues lose their characteristics and become simple or undifferentiated. Apart from its occurrence in metamorphosis, de-differentiation is seen when an organism breaks down in adverse conditions, such as cold and scarcity. If the hydroid Obelia is kept in unpropitious environ ment, the polyp may collapse into an undifferentiated bag of cells, without mouth or tentacles. The cells lose their coherence and migrate to the base of the hydrotheca, being finally absorbed into the common stem. A similar de-differentiation is well illustrated by some Ascidians, and may be an adaptive method of surviving adverse conditions. It is also well known in the case of tissues that are cultivated in vitro, and the interesting fact has been demonstrated by Champy and others that if the de-differentiated isolated tissue be re-planted in an appropriate living organism, re-differentiation may occur. (See DEDIFFERENTIATION.) A third use of the term degeneration is for the retrogressive changes that occur during senescence, or when an organ like the thymus gland undergoes reduction of function, or when a nerve ganglion is over-fatigued, as in the brain-cells of the short-lived summer bee.
(J. A. Tn.) DEGGENDORF or DECKENDORF, town of Bavaria, Germany, 25 m. N.W. of Passau, on the left bank of the Danube, which is there crossed by two iron bridges. Pop. It is at the lower end of the beautiful valley of the Perl bach. The old town hall dates from 1566. The church of the Holy Sepulchre, built in 1337, attracts thousands of pilgrims to its Porta Caeli or Gnadenpforte (Gate of Mercy) opened an nually on Michaelmas eve and closed again on Oct. 4. The town is a depot for the timber trade of the Bavarian forest, a station for Danube steamboats and the seat of several mills, breweries, etc. On the bank of the Danube outside the town are the remains of the castle of Findelstein; and on the Geiersberg (1243 ft.), in the immediate vicinity, stands another old pilgrimage church. About 6 m. N. is the village of Metten, with a Benedictine mon astery founded by Charlemagne in 8o1, restored as an abbey in 184o by Louis I. of Bavaria, and well known as an educational institution. The first mention of Deggendorf occurs in 868, and it appears as a town in 1212. Henry (d. 129o) of the Landshut branch of the ruling family of Bavaria made it the seat of a custom—house; and in 1331 it became the residence of Henry III. of Natternberg (d. . In 1337 a wholesale massacre of the Jews, who were accused of having thrown the sacred host of the church of the Holy Sepulchre into a well, took place in the town; and it is probably from about this date that the pilgrimage above mentioned came into vogue. The town was captured by the Swedish forces in 1633, and in the war of the Austrian Succession it was more than once laid in ashes.
See Gruber and Muller, Der bayerische Wald (Regensburg, 1851) ; Das Kloster Metten (Straubing, 1857) ; Mittermuller, Die hell. Hostien and die Jiiden in Deggendorf (Landshut, 1866).
DE GOEJE, MICHAEL JAN: see GOEJE, MICHAEL JAN DE.