Data from the analyses of twins and other observations indicate that opposite-sex twins have personality structures similar to

identical twins or fraternal same-sex twins. The traits observed include the following: (i) confusion of self representation and object representation; (ii) the tendency toward the use of primary-process thinking; (iii) libidinal attachment and intense hate toward the twin, an exaggeration of sibling love and rivalry; (iv) the prominent use of displacement, identification, and projection as defenses; (v) displacement of feeling toward the twin to other persons, resulting, for instance, in an adhesive transference; (vi) displacement of feelings from the parents to the twin and a related difficulty in resolving the oedipus complex; (vii) superego deficiencies.