The report explains how twin-studies may affect the science of population, both directly by their frequency and determining factors, and indirecdy in as much as twins provide a useful research method to study the physical and psychological traits which identify a human population.

It is possible, in fact, through the method of intrageminal-in-tergeminal comparison and through other methods, to study the population's normal and pathological traits.

As far as diseases are concerned the twin method affords the chance to discover or to reassert the hereditary nature of many diseases as well as the hereditary aspects of morbid receptivity and reactivity in the esogenous diseases; furthermore, it is possible to probe deeper while studying hereditary diseases especially in the fields of phenogenesis, variability and nosological classification.

The study of psychological traits in twins makes it possible to identify the instinctive tendencies and the hereditary components of the mental functions; also the study of learning capacity and of psycho-somal phenomena based on heredity.

In order to make it easier to complete twin studies on an increased number of twin sets, statistical surveys and social provisions of various kinds in favor of twins (which already have yíelded good results in Italy) are advocated.

The Authors have studied 56 twin pairs (31 MZ and 25 DZ) under the aspect of the psychomotor reactions they have shown while watching motion pictures. The most closely considered reactions have been head posture, arm and leg posture and mimic reactions. The analysis of the reactions was carried out on photographs taken during the projection of the films and then compared for the degree of similarity of the postural or mymical reactions. The degree of similarity was rated according to the following scale: concordant, similar, dissimilar, discordant.

The results obtained have shown that head posture (on which the influence of conscious mobility is higher) the hereditary factors have a clear influence; while for arm posture and especially for leg posture during projection the influence of hereditary factors could not be proven in any appreciable degree; this finding is thought to be related to the low influence of conscious mobility and with the sitting position being conditioned by environmental factors.

For mimic reactions the influence of a hereditary component is always clear, but from this point of view a marked difference is found between mimic reactions to anxiogenous and to comical films. Reactions to the latter reveal a higher, characteristic degree of difference between MZ and DZ twin pairs, i. e. a higher degree of hereditary influence.

The Authors have made further studies on the family trees under the aspects of previous twinnings and of previous personal pathological anamnesis, increasing the known case histories and strenghtening the conclusions reached by Gedda in previous studies.

A film has been made of 8 pairs of monozygotic and 4 pairs of dizygotic twins regarding their expression and behaviour, and we tried to examine their behaviour on genetical characters.

We do not agree, that all telencephalitic action is under control of the individuals' arbitribum; instead we stress that genetical characters are also important components.

A « plastic » adaptation to the given circumstances of the surroundings is provided by the qualitative and quantitative manyfoldednes of the telencephalon. The actions of man appear to be much more of free will than they really are.

There are abnormal states leading to diseases that are not confined to lesions or functional defects of particular organs but that are best interpreted from a broader view as result of deficient homeostatic mechanisms. Constitutional diabetes mellitus, hypertension and obesity belong to this category. The respective homeostatic defect involves the function of many organs and is genetic in nature. In contrast tp these constitutional states diabetes, hypertension and obesity can develop also as manifestation of localized and well defined diseases of any one of the organs which are links in the chain securing the respective homeostasis. These much less common disease types are symptomatic diabetes, hypertension or obesity. There is reason to assume that the constitutional types have a multifactorial (polygenic) causation which makes further elucidation of the mode of hereditary transmission very difficult.

In recent years various surgical procedures have been attempted to improve the cerebral function of mentally retarded or cerebral palsied children. One of these is the anastomosis of the carotid artery and jugular vein in an effort to improve the cerebral blood flow. This has been reported to have some degree of success, but the results are of questionable value because of the necessary lack of suitable controls. In this paper are presented the case histories of such an operation on identical twins, one operated and the second serving as a perfect control.

The family history of the twins was significant in that there was a strong history of mental disease on the father's side. Several members of his family had been confined to mental institutions. No clinical diagnoses are known but at least one was known to be a sexual pervert. The father had been in a mental institution before and after the birth of the twins and had received electric shock therapy, with no demonstrable improvement. He also was a sexual pervert. The parents were divorced when the twins were twenty months old. Before and after the divorce the twins and their mother were subjected to physical violence by the father. The twins were said to be extremely fearful of the father. There were no other children, and no other pregnancies.

Pregnancy was uneventful. Delivery was at term following a five day labor. Donald, the twin who was subsequently operated, was born first with a birth weight of six pounds, seven ounces. David, born a few minutes later, weighed six pounds, eight ounces.

After having stressed the importance of the hereditary problem in the field of dento-maxillary orthodontics, the A. considers hereditary evidence of the dento-maxillary anomalies and gives a review of literature on the subject.

He further considers the dento-maxillary anomalies trasmitted by genes, dominant and recessive, conected with sex and finally a few cases treated by him personally.

They are cases of family and twin, hypodontia, macrodontia, rotation and twisting, bad positions, hypodevelopment of a halfarcade, prognathism and overbite.