Erogenous zone

“ The anus would, however, seem to be sometimes an erogenous zone even at an early age. Titillation of the anus appears to be frequently pleasurable in women; and this is not surprising considering the high degree of erotic sensitivity which is easily developed at the body orifices where skin meets mucous membrane. (Thus the meatus of the urethra is a highly erogenous zone, as is sufficiently shown by the frequency with which hair-pins and other articles used in masturbation find their way into the bladder.) ”

“ If the excitation of erogenous zones increases the sexual tension, it can only be due to the fact that the erogenous zones are connected with these centers by previously formed anatomical connections. They increase there the tone of the excitation, and with sufficient sexual tension they set in motion the sexual act, and with insufficient tension they merely stimulate a production of the sexual substance. ”

“ Physiologically, what are known as "erogenous zones"—tissue which is capable of what in mature life is sexual excitation—are diffused through the organism. As the child passes through the "latent period" of later childhood and adolescence, these "erogenous zones" are concentrated as it were in the organs which are to serve the purpose of reproduction. If for any reason this process of concentration is checked, and remains in later life incomplete, the mature individual will be afflicted with certain tendencies to sex perversion. ”

“ These specific nuclear substances, different for each cell, are accumulated also in the nuclei of the germinal substance, constituting what Rignano calls the central zone of development. That is to say, each functional adaptation changes slightly the dynamical equilibrium of the organism, and this change in the system of distribution of the nervous currents leads to the deposit in the central zone of development of a new specific substance. ”

“ The physical causes of zonation are by far the most important. They arise from differences in temperature, water, and light. In the large, temperature differences are the most important, producing the great zones of vegetation. In a particular region or habitat, variations of water-content and humidity are controlling, while light, as shown above, is important in the reactions of forest and thicket. Physical factors produce zonation in a habitat or a series of habitats, when there is either a gradual and cumulative, or an abrupt change in their intensity. ”

“ Eudorina, however, has attained to "binary sex," for the female cells are the ordinary vegetative cells, at most a little enlarged, and the male cells are formed by ordinary cells producing a large flat colony of sixty-four minute males or sperms. In some cases four cells at the apex of a colony are spermogonia, producing each a brood of sperms, while the rest are the oospheres. The transition to Volvox must have arisen through the sterilisation of the majority of cells of a colony for the better nutrition of the few that are destined alone for reproduction. ”

“ The Equatorial zone, for instance, is characterized by extreme luxuriance in growth, owing no doubt to the great heat and abundant moisture therein, and exhibits a vegetation which is peculiar to itself, and which could only thrive under the hygrometric, thermometric, telluric, and other conditions of that extensive zone. ”

“ The purpose of the hairs, by the way, is to keep the little chamber moist, when the plant is left high and dry. If we watch the pores of the other warts carefully we may be fortunate enough to see the process of increase taking place, for it occurs outside the plant and not within the chamber. The egg cell divides into two and its contents pass out of the chamber by way of the pore; each cell of the male organs gives rise to sixty-four oval little structures, each provided with a pair of minute whip-like threads by means of which it swims from the chamber and goes in search of the egg cells. ”

“ Several leaf-traces are seen in transverse section in the secretory zone (black dots in fig. 148, A, sc; fig. 154, C, lt) : each trace consists of a strand of narrow tracheae accompanied by a few encircling layers of small parenchymatous cells. As a trace continues its steeply ascending course through the secretory zone, it becomes associated with a strand of that tissue and assumes the form of a collateral vascular bundle, the outer part of which does not consist of typical phloem but of shorter elements derived from the secretory zone. ”

“ Development of the male germinal glands.—These rudiments arise in exactly the same manner as those of the female. Sexual differentiation takes place in the later embryonic stages. We then notice that in the male four masses of genital cells become surrounded by epithelial cells. These masses, which form the germs of the four testicular follicles of Phyllodromia, stand in intimate union with the rudiment of the vas deferens, and in the later stages move in connection with the latter, away from and behind the original genital rudiment. ”

“ The most important change which has been effected concerns the ridges connecting the successive grooves. A lumen has appeared in each of these, which seems to open at both ends into the adjacent grooves. At the same time the cells, which previously constituted the ridge, have become (except where [Pg 621] they are continuous with the walls of the grooves) partially constricted off from the germinal epithelium. The ridges, in fact, now form ducts situated in the stroma of the ovarian ridge, in the space between the Wolffian duct and the germinal epithelium. ”

“ Twice in the twenty-four hours the littoral zone is covered by water and exposed to the direct rays of the sun or the cooling effects of the night. There is a great range of temperature; mechanical agencies produce their maximum effects,” [171] and physical conditions in general are most varied. Still greater diversity is introduced by the fact that the zone is inhabited by both marine and terrestrial organisms, while the evaporation of the sea-water which flows over tidal marshes and lagoons leads to the formation of saline deposits. ”

“ The remainder of the stroma of the ovarian ridge has now acquired a definite structure, which remains constant through life, and is eminently characteristic of the genital ridge of both sexes. The bulk of it (Pl. 24, fig. 3, str) consists of closely packed polygonal cells, of about 0.014 mm. with large nuclei of about 0.009. These cells appear to be supported by a delicate reticulum. The whole tissue is highly vascular, with the numerous capillaries; the nuclei in the walls of which stand out in some preparations with great clearness. ”

“ CAUSES OF ZONATION 333. Growth. The causes that produce zones are either biological or physical: the first have to do with some characteristic of the plant, the second with the physical features of the habitat. Biological causes arise from the method of growth, from the manner of dissemination, or from the reaction of the species upon the habitat. The formation of circles as a result of radial growth is a well-known occurrence with certain plants, but it is much more common than is supposed. ”

“ At certain times, one or two sets of germinal cells fail to produce ova; the epithelial wall of the ovary thickens round these cells, so that they become incompletely separated from the rest in a so-called “nutrient chamber” (Fig. 15, B, N.C) . Germ-cells enclosed in a nutrient chamber degenerate and are ultimately devoured by the ovarian epithelium. The significance of these nutrient chambers is unknown.
45
Fig. ”

“ In the lower (or simpler and possibly degenerate Metazoa) the reproductive or germinal tissue consists of a few cells, sometimes in a group, sometimes scattered and sometimes migratory; in the vast majority of the Metazoa the germinal tissue becomes aggregated in distinct organs, of which those that give rise to ova or female gametes are known as the ovaries, and those that give rise to the spermatozoa or male gametes are known as the testes. The ovary and the testis are the primary reproductive organs ”

“ These secondary centres have in common the fact that they always involve the entrances and the exits of the body—the regions, that is, where skin merges into mucous membrane, and where, in the course of evolution, tactile sensibility has become highly refined. It may, indeed, be said generally of these frontier regions of the body that their contact with the same or a similar frontier region in another person of opposite sex, under conditions otherwise favorable to tumescence, will tend to produce a minimum and even sometimes a maximum degree of sexual excitation. ”

“ The zones of growth are commonly not piled exactly over each other, but rather obliquely, as represented in fig. 4 b. Each zone projects, forming a prominent, sharp, toothed ridge round the shell. In Coronula (Pl. 16, fig. 6) and its allies, the outer lamina of the wall is formed by the union, a little above the basal margin, of ledges running along the sides of the longitudinal septa. In Xenobalanus (Pl. 17, fig. 4 c) similar ledges are less perfectly joined, and apertures seem always to be left in transverse rows under the transverse toothed ridges, which latter are best seen in fig. ”

“ The surface of the ovarian region is somewhat irregular and especially marked by deep oblique transverse furrows. It is covered by a distinct, though still irregular pseudo-epithelium, which is fairly columnar in the furrows but flattened along the ridges. The cells of the pseudo-epithelium have one peculiarity very unlike that of ordinary epithelial cells. Their inner extremities (vide fig. 10) are prolonged into fibrous processes which enter the subjacent tissue, and bending nearly parallel to the surface of the ovary, assist in forming the tunic spoken of above. ”

“ Until the fifth or sixth week the development of the genital ridge is very much the same in the two sexes, and consists of cords of cells growing from the epithelium-covered surface into the mesenchyme, which forms the interior of the ridge. In these cords are some large germ cells which are distinguishable at a very early stage of development. ”

“ At the same time the solutions in the upper zone are quite certainly more dilute than those below. The horizon of greatest solution lies between the surface and a level slightly below the ground-water surface, or, in other words, in the zone where atmosphere and hydrosphere coöperate. Surface-waters are charged with atmospheric and organic acids and other solvents, and their general effect upon the rocks is markedly solvent down to or often below the permanent water-level. ”

“ In connexion with the structure of the ova, the ovaries themselves and the oviducts are built upon the Sauropsidan plan. In the male the testes retain the primitive abdominal position. The fact that the urinary and genital products escape by means of their ducts into a chamber which also receives the end of the alimentary tract is not a distinctive feature of this group, inasmuch as it is seen in the Marsupials, and also in certain low Eutheria, such as the Beaver and other Rodents, and a few Insectivores. ”

“ In the initial stages of a succession, as well as in the transitions between the various stages, the plant population is so scattered, so transient, or so dense as to respond not at all to a degree of symmetry which produces marked zonation in later formations. The alternation of conspicuous species not only causes great interruption of zones, but often also completely conceals the zonation of other species, such as the grasses, which, though of more importance in the formation, have a lower habit of growth. ”

“ Some authorities think that "every cell in the body is an organ of internal secretion", [2] and that thus each influences all the others. The sex glands are especially important as endocrine organs; in fact the somatic cells are organized around the germ cells, as pointed out above. Hence the sex glands may be considered as the keys or central factors in the two chemical systems, the male and the female type. ”

“ Perhaps the most remarkable of all somatic sexual characters are those which are almost universal in the whole class of Mammalia, the mammary glands in the female, the scrotum in the male. We have considered the evidence concerning the relation of the development and functional action of the milk glands to hormones arising in the ovary or uterus, now we have to consider the origin of the glands and of their peculiar physiology in evolution. ”

“ We have seen that after the two maturing divisions in the egg-cell have been accomplished the ovum no longer contains a mechanism of division, as the centrosphere breaks up after the second division; embryonic development can therefore only begin when a new centrosphere has been introduced into the ovum, and this is normally brought about by fertilization, that is, by the entrance of the sperm-cell, whose nucleus is accompanied by a centrosphere. ”

“ Nearly all the Platyhelminthes are HERMAPHRODITIC, and in nearly all there are, in addition to the ovaries producing ova, other glands attached to the female genital apparatus, namely, the vitellaria or yolk glands, which provide a substance termed yolk, which serves as nourishment for the embryo. The fully formed eggs have shells and are “compound,” i.e., composed of the egg or ovarian cell, which is surrounded by numerous yolk cells or their products of disintegration. ”

“ If at the time of rutting a single ovum is detached from the ovary, and descends slowly through the genital canal (animals which bear a single offspring) , fertilization taking place at the beginning of the rutting suffices to produce a female, and at the end of the rutting to produce a male, provided that the change in the condition of the ovum takes place normally during its passage through the genital canal. ”

“ On the later stages of development of the ovary I have no complete series of observations. The yolk spherules I find to be first developed in a peripheral layer of the vitellus. I have not been able definitely to decide the relation of the zona radiata to the first formed vitelline membrane. Externally to the zona radiata there may generally be observed a somewhat granular structure, against which the follicle cells abut, and I cannot agree with Waldeyer (loc cit., p. 40) that this structure is continuous with the cells of the discus, or with the zona radiata. ”