Transmission of many of these cerebral defects occurs at the moment of conception. The embryonic mechanism of these defects, and the influence which foetal and maternal impressions and injuries exert on the development of the nerve centres, furnish valuable argument by analogy in support of conclusions regarding the degeneracy group. Embryologists imitate known natural teratological states of the nerve centres by artificial methods. By wounding the embryonic and vascular areas of the chick's germ with a cataract needle malformations are induced, varying in intensity and character with the earliness of the injury and its precise extent. More delicate injuries produce less monstrous development. It is particularly the partial varnishing or irregular heating of the egg-shell that results in the production of anomalies comparable to microcephaly and cerebral asymmetry. The constancy of the injurious effect of so apparently slight an impression as the partial varnishing of a structure not directly connected with the embryo at all, suggests a most plausible explanation of maternal and other impressions acting on the germ. The delicate problems in this connection may be inferred from the observations of Dareste that eggs transported in railroad cars, and thus subject to the vibration and repeated shocks of a railroad journey, are checked in development for several days. A less coarse molecular transmission taking place during the maturation of the ovum or its fertilisation, or, finally, during the embryonic stages of the more complex and hence more readily disturbed and distorted human germ, would account for the disastrous effects of insanity, emotional explosions, and mental or physical shocks of either parent on the offspring. For the majority of cerebral deformities the causes of the deformity must exist in the germ prior to the appearance of the separate organs of the body. Artificial deformities produce analogous results because they imitate original germ defects either by mechanical removal or by some other interference with a special part of the germ. Early involvement of the germ is shown in the fact that the somatic malformation in degeneracy often involves other parts of the body than the nervous axis: defective development of the uro-genital system, deformities in the face, skull, irregularities of the teeth, misshapen ears and limbs.