BRYOLOGY). If a hydra is deprived of its tentacular ring and inserted with this cut surface into the side of another hydra, nearly all the trunk of the former can be removed, without pre venting the inserted head region from drawing material from the side of the larger component, the head "dominating" the flank. In planarians, newts and tadpoles, regeneration-buds in a suffi ciently early stage will develop into any structure, in place of which they have been grafted. Such a regenerating "blastema" derived from the tail of a newt will develop into a limb if grafted on the cut stump of the latter. But in the lizard the regenerating tail blastema is not changed, even if grafted in place of a fore-leg (see HETEROMORPHOSIS and REGENERATION IN ANIMALS).
As soon as differentiation sets in, the regenerating tissues will no longer be influenced by the site on which they are grafted. They then conform to the general rule, that the form of a body region or organ will not be changed by transplantation. Eyes may not only be grafted into eyesockets, but also to the neck or back of salamanders; the main difference being, that in the case of "replantation" function may be restored, whereas "deplanta tion" to an abnormal situation makes restoration of sight impos sible. The orientation in which the components meet is only of consequence for function, not for morphology. When the poste rior half of a tadpole is joined to the anterior of another in normal orientation, all parts will be able to function. If, on the contrary, two posterior halves are joined with their anterior cut surfaces together, the compound will not be able to take in food, as a mouth is lacking and will not be formed. If anterior halves are joined by their posterior cut surface, the two heads will pull in opposite directions and often tear asunder. The orientation of the grafted parts towards each other need not only be "normal" or "opposite," as in our last mentioned examples. Two animals, grafted on to each other with their backs or bellies united, are termed "inverted" grafts. If a limb be cut off and, after removal of its distal tip, grafted with the latter end directed towards the body, we have an instance of "reversed" transplantation. In hydras other possibilities of grafting have been invented : if the body be slit lengthwise, the animal can be unrolled completely. By putting one unrolled hydra on the other with their interior sides towards each other, and pinning the edges together for a short time, the two hydras will be united lengthwise by this "conplantation." By turning one hydra inside out and inserting it into the body-channel of a second polyp an "association" is effected. Finally by pressing hydras through a cloth and mixing the dissociated parts complex hydras of "mosaic" character were obtained.
When two different kinds or species of fresh-water polyp have been grafted, the behaviour of the compound as regards asexual reproduction by budding can be studied. Although both kinds used may enter into a bud, in time the specific tissues will sepa rate and no permanent "chimera" can be created. Such experi ments are especially striking when the two species differ in colour.
In higher animals without asexual reproduction, buds of chi merical character may be obtained by grafting regenerating tissue, for instance from the member of a black axolotl on to the regener ating member of a white specimen. If in this way half of the regenerating bud has been changed, the leg will show a "sectorial chimera." When the bud of one type is overgrown by the skin of the host, a "periclinal chimera" results. In any case each cell only produces cells with the character of the species or race it has been taken from, as in "mosaic chimeras" with irregular mixture.