In many cases of excess of parts the extra part or member is manifestly derived from the same ovum, and even the same part of the ovum, being merely the effect of a redundancy and vagary of growth. Such cases include most instances of extra digits or other organs, and even of double monsters, as manifested by the fact that such extra organs grow from the normal identical organs. Hence the extra digit is attached to the normal digit, the extra head to the one neck, the extra tail to the croup, extra teeth to the existing teeth, and even two similarly formed bodies are attached by some point common to both, as the navels, breastbones, backs, etc. (Pl. XIX, figs. 1, 2, 3.) This shows that both have been derived from the same primitive layer of the embryo, which possessed the plastic power of building up a given structure or set of organs. An inclosed ovum, on the other hand, has no such identity or similarity of structure to the part with which it is connected, showing an evident primary independence of both life and the power of building tissues and organs. The power of determining extra growth along a given natural line is very highly developed in the early embryo and is equally manifest in the mature examples of some of the lower forms of animal life. Thus a newt will grow a new tail when that member has been cut off, and a starfish will develop as many new starfishes as the pieces made by cutting up the original one. This power of growth in the embryo and in the lower form of animals is comparable to the branching out again of a tree at the places from which branches have been lopped. The presence of this vegetablelike power of growth in the embryo accounts for most double monsters. The influence of disease in modifying growth in the early embryo, increasing, decreasing, distorting, etc., is well illustrated in the experiments of St. Hilaire and Valentine in varnishing, shaking, or otherwise disturbing the connections of eggs and thereby producing monstrosities. One can easily understand how inflammations and other causes of disturbed circulation in the womb, fetal membranes, or fetus would cause similar distortions and variations in the growing fetus. It is doubtless largely in the same way that certain mental disturbances of a very susceptible dam affect the appearance of the progeny. The monstrosities which seriously interfere with calving are mainly such as consist in extra members or head, which can not be admitted into the passages at the same time, where some organ of the body has attained extra size, where a blighted ovum has been inclosed in the body of a more perfect one, or where the body or limbs are so contracted or twisted that the calf must enter the passages doubled up.