This volume is the outcome of a course of five lectures on “Regeneration and Experimental Embryology,” given in Columbia University in January, 1900. The subjects dealt with in the lectures are here more fully treated and are supplemented by the discussion of a number of related topics. During the last few years the problems connected with the regeneration of organisms have interested a large number of biologists, and much new work has been done in this field; especially in connection with the r

Although a few cases of regeneration were spoken of by Aristotle and by Pliny, the subject first attracted general attention through the remarkable observations and experiments of the Abbé Trembley. His interest was drawn to certain fresh-water polyps, hydras, that were new to him, and in order to find out if the organisms were plants or animals he tried the effect of cutting them into pieces; for it was generally known that pieces of a plant made a new plant, but if an animal were cut into piec

There is a constant interchange of material and of energy that takes place between a plant or an animal and its surroundings, and this interchange may be influenced by such physical conditions as temperature, light, gravity, etc., or by such chemical conditions as the composition of the atmosphere or of the water surrounding the organism. We can study the process of regeneration either by keeping the regenerating organism under the same conditions that it is subject to in its natural environment

The comparatively few cases in animals in which regeneration has been shown to be influenced by external factors have been given in the preceding chapter. In all other cases that are known the factors are internal. By this is meant that we cannot trace any direct connection between the result and any of the known external agents that have been shown in other cases to have an influence on regeneration. Certain external conditions must, of course, be present, such as a supply of oxygen, a certain

The series of experiments that Vöchting has carried out on the regeneration of the higher plants are so much more complete than all previous experiments, and his analysis of the problems concerning the factors that influence regeneration is so much more exact than any other attempts in this direction, that we may profitably confine our attention largely to his results. Many of his experiments were made with young twigs or shoots of the willow (salix), which, after the removal of the leaves, were

There is a widespread belief amongst zoologists that a definite relation exists between the liability of an animal to injury and its power of regeneration. It is also supposed that those individual parts of an animal that are more exposed to accidental injury, or to the attacks of enemies, are the parts in which regeneration is best developed, and conversely, that those parts of the body that are rarely or never injured do not possess the power of regeneration. Not only do we find this belief im

It is a more or less arbitrary distinction to speak of internal in contrast to external organs, since the latter contain internal parts; but the distinction is, for our present purposes, a useful one, especially in regard to the question of regeneration and liability to injury. In this connection we shall find it particularly instructive to examine those cases of regeneration of internal organs that cannot be injured, under natural conditions, without the animal itself being destroyed. An illust

During the normal life of an individual many of the tissues of the body are being continuously renewed, or replaced at definite periods. The replacement of a part may go on by a process of continuous growth, such as takes place in the skin and nails of man, or the replacement may be abrupt, as when the feathers of a bird are moulted. It is the latter kind of process that is generally spoken of as physiological regeneration. In the same animal, however, certain organs may be continually worn away

Self -division, as a means of propagation, is of widespread occurrence in the animal kingdom. In some cases the animal simply breaks into pieces and subsequently regeneration takes place in the same way as when the animal is cut into pieces by artificial means. In other cases the parts are gradually separated, and during this time new parts are formed by a process resembling that of regeneration after separation. A few zoologists have tried to show how the process of regeneration before separati

By uniting parts of the same or different animals, or of plants, there is given an opportunity of studying a number of important problems connected with the regeneration of the grafted parts. Trembley’s experiments in grafting pieces of hydra are amongst the earliest recorded cases of uniting portions of different animals, although in plants the process of grafting has been long known. [77] Trembley found that if a hydra is cut in two, the pieces can be reunited by their cut-surfaces, and a comp

There are many difficulties in the way of determining the origin of the cells that make up the new part. The only means at present at our command for studying their source is by serial sections of a number of different stages taken at intervals from different animals. Since there may be differences between the processes in different individuals, and since we can only piece together the information gained from successive stages, much uncertainty exists in regard to the changes that take place dur

Not only do adult organisms have the power of regeneration, but embryos and larval forms possess the same power, and even portions of the segmenting, and also the unsegmented, egg may be able not only to continue their development, but in many cases to produce whole organisms. Haeckel observed in 1869-1870 that pieces of the ciliated larvæ of certain medusæ, and even pieces of the segmented egg, could produce whole organisms. The more recent experiments of Pflüger (’83) and of Roux (’83) on the

The experimental work that Pflüger carried out in 1883 on the effect of gravity on the cleavage of the frog’s egg, and the conclusions that he drew from his experiments, mark the starting-point for the modern study of experimental embryology. [124] We can trace the influence of Pflüger’s results through most of the more recent work, and one of the conclusions reached by Pflüger, namely, that the material of the egg may be divided by the cleavage planes in any way whatsoever without thereby alter

It is significant to find that the theory of pre-formation of the embryo in the egg, that was so very widely held during the seventeenth and eighteenth centuries, and during the first part of the nineteenth century, was at once applied to the explanation of the regeneration of animals when this process became known. Bonnet in 1745 attempted to explain the newly discovered facts in regard to the regeneration of animals by means of the pre-formation theory. Just as the egg was supposed to enclose

In the preceding chapters certain matters had to be taken for granted, since it was not possible, or desirable, at the time to discuss more fully some of the terms that are in common use, or to analyze more completely many of the phenomena. It was also not necessary to give the general point of view under which the phenomena were considered in their physical, chemical, or even causal connection. Little harm has, I trust, been done by relegating such questions to the final chapter. An attempt wil

Aldrovandus, Ulysses. 1642. Historia Monstrorum. MDCXLII. Cap. VIII. 1645. Patritii boloniensis de quadrupedibus digitatis oviparis. Lib. II. Boloniae, MDCXXXXV. Allman, J. A. ’64. Report of the present State of our Knowledge of the Reproductive System in the Hydroida. Report of the 33d Meeting of the British Assoc., 1864. Andrews, E. A. ’90. Autotomy in the Crab. The American Naturalist, XXIV, 1890. ’91. Report upon the Annelida Polychaeta of Beaufort, North Carolina. Proc. U. S. National Museu