Secondary Sexual Characteristics

SECONDARY SEXUAL CHARACTERISTICS, a term used in various meanings and designating: 1) all signs by which one sex differs from another, except for the sex glands (the latter are primary sexual characteristics); 2) all sexual signs, except those having a direct relation to sexual reproduction (sexual organs); 3) all parts of the sexual apparatus, except the sex glands (sometimes only the ducts and accessory glands); 4) only the external parts of the sexual apparatus (copulatory apparatus). With the 3rd and 4th meanings of this term, in addition to secondary signs, tertiary, and sometimes quaternary signs, etc., are also accepted. The 2nd definition of S. s. c. is the most common, while the 1st is the most accurate, as it most sharply defines the boundary between primary and S. s. c. It is much more difficult to draw the boundary when accepting the 2nd definition. The division into secondary, tertiary, and quaternary signs, based on a greater or lesser connection of signs with sexual reproduction, is even more artificial. In these cases, the boundary between S. s. c. and tertiary signs usually passes at the same place where it passes between primary and secondary signs in the 2nd meaning of these concepts; the boundary between tertiary and quaternary signs is completely arbitrary: for example, in insects, sensory organs are referred to as tertiary, and pigmentation, locomotor organs, etc., as quaternary; to determine the greater or lesser importance for sexual reproduction of these various organ systems, given the completely peculiar function of each individual system, is extremely difficult. The indefiniteness of the expression S. s. c. leads to the fact that some authors completely abandon this term, others apply it with reservations or try to give another classification of sexual signs. The attempt to subdivide sexual signs on the basis of their relation to sexual reproduction (Pohl) gives the same division into primary, secondary, tertiary, etc., signs, but under other names. Experiments on the dependence between the sex gland and other sexual signs gave a certain basis for the term S. s. c., at least for part of animals; they also made it possible to introduce a more substantiated classification of these signs on the basis of their relation to the hormones of the sex gland. The dependence between sex glands and other sexual signs was determined by: 1) castration; 2) transplantation of sex glands from an individual of one sex to an individual of the other sex, previously castrated; 3) transplantation of organs bearing S. s. c. from an individual of one sex to an individual of the other sex; 4) removal of the rudiment of an organ bearing S. s. c., after transplantation into a given individual of sex glands of the other sex and observation of its regeneration (experiments, mainly of Kopetz and Meisenheimer on insects, Zavadovsky and others on vertebrates). These experiments can be divided into 2 groups according to their results: 1) the sex gland has no influence on S. s. c. (insects), and 2) S. s. c. are dependent on the hormones of the sex glands (vertebrates, some worms). In the second group of experiments it was revealed that: 1) upon castration of both males and females, a more or less uniform form is obtained; 2) upon castration only some S. s. c. change, others remain unchanged, for example, the plumage of male birds does not change, but in females it takes a male form; 3) upon transplantation of sex glands of the other sex, after preliminary castration, sex transformation occurs; 4) upon transplantation of an individual organ of the other sex, this organ changes its structure, corresponding to the sex of the individual to which it is transplanted. From these experiments it follows that the difference between the sexes depends on the action of the hormones of the sex glands on certain organs. In this case, a certain peculiarity can be acted upon by either male or female hormones (comb of chickens, instincts) or only by hormones of one sex (plumage of birds-female hormones, beard and mustache in man-male hormones). In addition to sexual differences caused by hormones, some authors also note independent signs, as a result of which castrates of both sexes always differ somewhat from each other. An undeniable such sign is the difference in chromosomes: for example, in birds there are X- and Y-chromosomes in females, and in males two X-chromosomes, in mammals the opposite. Data from this group of experiments show that for known groups of organs the name 'S. s. c.' has a basis: they depend on the 'primary sign'-the sex gland. Zavadovsky divides S. s. c. as follows: 1) pseudo-sexual (independent)-develop without the participation of the sexual hormone; the difference between the two sexes depends on the fact that the development of such a sign is inhibited by the hormone of the other sex (for example, plumage and spurs of a rooster); 2) eu-sexual (dependent) signs--arise under the action of the sexual hormone (comb of chickens, instincts, beard and mustache of a man, etc.); 3) somo-sexual-do not depend on sexual hormones; the difference of sexes is the result of the difference in cells of a given organ in the male and female (secondary-sexual signs of insects). In their mutual relations, all sexual signs of the last type are completely equivalent and independent; in this case the division into primary and S. s. c. is possible only on the basis that S. s. c. are phylogenetically later. Proponents of the 'pubertal gland' theory single out the endocrine sex gland as the primary cause, subdividing the sex gland into an endocrine part and sex cells. Lipschütz divides the other sexual signs by functions; this same division is adhered to by Meisenheimer, both authors refusing the term S. s. c. The so-called 'sex-linked' (sex-linked) signs should be set apart; Russian authors sometimes incorrectly call them 'limited by sex'. In some cases, usually in the heterozygous (see Heterozygotes) sex, differences from the basic type are noted [pale coloration in Abraxas, color blindness, hemophilia (see) in men]. Such signs Zavadovsky calls concordosexual. These last signs can be called sexual only conditionally, since they can be in certain conditions in the other sex; moreover, lines can be drawn in which both sexes possess these signs.