The Authors take once more into consideration the problem of the hereditary nature of twinning on the basis of their own studies and of recent findings on human twinning induced by human menopausal gonadotropin (HMG).

Personal studies concern 3,221 cases of twinning drawn from the special files (“Gemelloteca”) of the Mendel Institute. On the basis of this material the Authors state that the occurrence of the cases of twinning in the paternal and maternal ascendancies of the twin index cases is significantly more frequent than would be expected in proportion to the frequency of twinning events in the Italian population.

This finding is in agreement with the hypothesis of the hereditary nature of the twinning phenomenon.

The same material is used to compare the frequency of twinning in the paternal and maternal families of twins. The observed frequency in the maternal families is significantly higher than in paternal families in which the frequency approximates population values. This finding leads the Authors to formulate the hypothesis that the twinning trait is limited to the female sex and is presently manifested by the occurrence of twins in the next generation. Thus studies on the frequency of twinning as a hereditary phenomenon should be based on the families of the mothers of twins.

Original studies also concern the 1,105 triplet sets born in Italy in the years 1952-1961. A study of the experimental and theoretical distribution of sex combinations in this triplet material allowed the Authors to prove that the experimental distribution differs from the theoretical one, based on the hypothesis of independence of the two types of zygosity (MZ and DZ). The absence of independence is considered a proof of the hereditary singleness of twinning.

The Authors further take into consideration cases of twinning induced in sterile women by administration of human menopausal gonadotropin (HMG): they observe that cases reported to date seem to be limited to dizygotic or plurizygotic twinning. These findings lead the Authors to believe that in this case hypophyseal FSH, responsible for ovulation, fails to find the usual pathway leading to standard uniparous pregnancy in the human species; the mechanism involved in such pathway is the object of some hypotheses of a hormonal nature. The Authors also believe that FSH stimulates not only the follicle but also follicular gametogenesis and even perhaps the division of the fertilized egg resulting in MZ twinning.

The authors report on six patients exhibiting a congenital heart disease and malformations of the upper limbs. In two of them this association is similar to that described by Holt and Oram in 1960: atrial septal defect, heart arrythmia and abnormal thumbs. The other four patients have the same skeletal anomalies but different heart malformations. Dermatoglyphic studies revealed a high frequency of a distal position of the axial triradius and of an equivalent of a simian crease. The karyotypes are all normal. The etiology is discussed.

A case of trisomy E with phocomelia of one arm is presented and the hitherto reported cases of trisomy E with phocomelia are listed. The different causes of phocomelia are discussed. Similarities and dissimilarities of the clinical picture of conditions associated with phocomelia are presented.

To determine the small population as a specific group, several quantitative indexes have to be taken into consideration. The author, making use of these indexes, differentiates three types of small populations: the isolate, the « dem » and the « large dem ». The central type — the dem — is a group including 1,500 to 4,000 individuals with an increase of more than 20-25 per cent in 25 years (one generation); a high proportion, about 80 per cent, of the marriages is concluded inside the group and an insignificant part of the members have descended from allogenous ancestors. The inhabitants of a rural locality constitute in most cases a « dem ». Theoretical calculations as well as genealogical studies have shown that the preponderant part of adult members of a « dem » appear to be related to each other in the eighth degree (according to Tab. 2 - cousins thrice removed).

Cytogenetic studies were performed in six clinically typical cases of Turner's syndrome. In five of them an XO chromosome complement was observed. In the sixth case the chromosome number appeared normal, but karyotype analysis revealed the presence of three large metacentric chromosomes similar to No. 3. A diagnosis of presumptive isochromosome for the long arm of X was suggested by the autoradiographic evidence of late replication and by the presence of larger than normal Barr bodies and drumsticks.

A man of 32 is described suffering from a combination of three disorders: cutis verticis gyrata, severe mental deficiency and aplasia of the thyroid. Four of his close relatives were also severely retarded. The possibility is discussed of the syndrome being inherited through an X-linked recessive gene.

Differential trends of R/L Symmetry as shown by the incidences of Symmetry (S) and Asymmetry (A) in Cummins' summational Main Line Index, as based on the Burman material (400 ♂ & 71 ♀) are slightly higher in females than in males. However, these are not statistically significant.

By grouping MLI values in two categories, (a)-5 or 〈 5 and (b)-6 or 〉 6, it is found that MLI values above 6 are largely involved (relative to 5 or 〈 5) in contributing to the incidence of asymmetric R/L combinations of MLI. Further, the male-female differences in the three combinations (a) & (a), (a) & (b), (b) & (b) are statistically significant.