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aboral animal annelids apical end appear archenteron arise autotomy basal end bilateral blasto blastomeres blastula body breaking-joint buds cleavage connection crustacea ctenophore cut-edge cut-end cut-surface digestive tract distal division earthworm ectoderm endodermal eration experiments explain factors formation gastrula germ-layers germs gland grafted grow growth half-embryo Hertwig hydra hydranth hydroid hypertrophy hypothesis individual influence injured half isolated blastomeres kind larvae later Loeb lumbriculus material ment mesoderm muscles natural selection nerve-cord normal notochord nucleus number of cells oral end organs peristome Pfliiger pharynx phenomena planarian plant polarity position posterior end posterior piece power of regeneration present process of regeneration produce protoplasm regen regeneration takes place removed roots Roux salamander sea-urchin segments self-division separated shown in Fig side small piece smaller sort species stage starfish stem stolons structure substances supposed symmetrical tadpole tail tentacles tion tissue totipotent tubularia Vochting whole embryo worm
Page 72 - and Plants under Domestication says : " In the case of those animals that may be bisected, or chopped into pieces, and of which every fragment will reproduce the whole, the power of regrowth must be diffused throughout the whole body. Nevertheless, there seems to be much truth in the view maintained by Professor Lessona
Page 164 - decreased in the course of phylogeny in correspondence with the increase in complexity of organization, but that it may, on the other hand, be increased by special selective processes in each stage of its degeneration in the case of certain parts which are physiologically important and at the same time frequently exposed to loss.
Page 165 - crystal, we say that the whole aggregate exerts over its parts a force which constrains the newly integrated molecules to take a certain definite form, we seem obliged, in the case of the organism, to assume an analogous force.
Page 165 - cut off ? Is it of the same order as the ability of an injured crystal to recomplete itself? In either case new matter is so deposited as to restore the original outline. And if, in the case of
Page 164 - Hence there is no such thing as a general power of regeneration ; in each kind of animal this power is graduated according to the need of regeneration in the part under consideration." " We are, therefore, led to infer that the general capacity of all parts for regeneration may have been acquired by selection in the lower and simpler forms, and that it has
Page 180 - It can be shown, I think, with some probability that the forming organism is of such a kind that we can better understand its action when we consider it as a whole and not simply as the sum of a vast number of smaller elements. To draw again a rough parallel; just as the properties of sugar are peculiar to the molecule and cannot be
Page 72 - that this capacity is generally a localized and special one serving to replace parts which are eminently liable to be lost in each particular animal. The most
Page 19 - regeneration " has come to mean, in general usage, not only the replacement of a lost part, but also the development of a new, whole organism, or even a part of an organism, from a piece of an adult, or of an embryo, or of an egg. We must include also those cases in which the part replaced is less than the part removed, or even different in kind.
Page 4 - Bonnet found that if a newly regenerated head is cut off, a new one regenerates, and if the second one is removed, a third, new one develops, and in one case this occurred eight times : the ninth time only a bud-like outgrowth was formed. In other cases a new head was produced a few more times, but never more than twelve.