Ovipositor

“ One of the most extraordinary instances of this kind of ovipositor is found in an Ichneumon-fly brought from Bogotá. The body, from the head to the end of the tail, is not quite an inch long, while the ovipositor is six inches and a half in length, and scarcely thicker than that of the insect whose portrait is given in the illustration. ”

“ In many instances the fertilizing principle is transferred from the body of the male to that of the female during flight, and, strange as it may seem, the intromittent organ of the male and the ovipositor of the female develop and continue only for that brief period which is necessary for the transference of the quickening principle and for the depositing of the egg in a place of safety. ”

“ From the observations made by Réaumur, he concluded that the mother-fly, above described, deposits her eggs in the flesh of the larger animals, for which purpose she is furnished with an ovipositor of singular mechanism. We have seen that the ovipositors in the gall-flies (Cynips) are rolled up within the body of the insect somewhat like the spring of a watch, so that they can be thrust out to more than double their apparent length. To effect the same purpose, the ovipositor of the ox-fly lengthens, by a series of sliding tubes, precisely like an opera-glass. ”

“ The gravid female always retains an upright position at this time, as indeed she does at other times. She is so absorbed in her task that she may readily be watched, even through a magnifying glass. The ovipositor, which is about four-tenths of an inch in length, is plunged obliquely and up to the hilt into the twig. ”

“ The female organs consist principally of the ovaries, the oviducts, the sperm-reservoir, and the ovipositor. In the ovaries the eggs are generated, and remain till rendered fit by impregnation, and the other circumstances necessary for their maturation, to pass through the oviducts. According to Mr. Hunter, what are called ovaries are really ducts; the eggs therefore are not formed as in other animals, in a cluster on the back, but in those ducts, of which there are six on each side. When full of eggs, they form a kind of quadrangle ”

“ In the different families of the Hymenoptera, there are various modifications of the ovipositor, in accord with the habits of the insects and the purposes to which the organ is put. The sting of wasps, ants and bees is a modified ovipositor and is used for egg-laying by the fertile females, as well as for defence. Most male Hymenoptera have processes which form claspers or genital armature. These processes are not altogether homologous with those of the ovipositor, being formed by inner and outer lobes of a pair of structures on the ninth abdominal segment. ”

“ The male, also, in some few cases differs from the female in possessing analogous organs, as the receptacles for the ova possessed by the males of certain fishes, and those temporarily developed in certain male frogs. Female bees have a special apparatus for collecting and carrying pollen, and their ovipositor is modified into a sting for the defence of their larvæ and the community. In the females of many insects the ovipositor is modified in the most complex manner for the safe placing of the eggs. ”

“ The form of the incision seems to be due to the necessity of placing the eggs in solid wood, avoiding the pith. In a number of instances where the incision had accidentally penetrated the pith, the furrow was left incomplete, and no eggs were deposited.
As may be supposed, ovipositing is attended with great labor on the part of the female. Each thrust of the ovipositor requires a severe and prolonged struggle; each furrow, judging by the number of displaced fibers, must require from twenty-five to forty thrusts; and each female makes many separate furrows. ”

“ Specimens are plentiful; and as the ovipositor in this insect is large, and easily broken up into its component parts, it may well serve as an introduction to the study of these organs in other Insects—the Saw-flies, for example.
When the insect is about to deposit her eggs, she selects a spot where the soil is light, and bending the ovipositor nearly at a right angle to her body, thrusts it into the ground as far as possible. Then, by a muscular effort, the plates of the ovipositor are separated, and several eggs travel down the passage formed by the central pair of rods into the hole. ”

“ In the female, each ovary consists of a large number of ovarian tubes, in which swollen chambers containing the egg-cells alternate with smaller chambers enclosing nutrient material. In connexion with the ovipositor are two poison-glands, one acid and the other alkaline in its secretion. ”

“ The ovipositor is long and prominent, enabling the female insect to lay her eggs in the wood of trees, where the white larvae, whose legs are excessively short, tunnel and feed. These insects are adorned with bands of black and yellow, or with bright metallic colours, and on account of their large size and formidable ovipositors they often cause needless alarm to persons unfamiliar with their habits. ”

“ When an ovipositor exists, the vaginal tube opens directly into it, forming a continuous canal a considerable way beyond the extremity of the body.
In the male the principal internal generative organs are the testes, vasa deferentia, vesicula seminalis, and ductus ejaculatorius: the external are the penis, and the prehensory organs connected with it.
Like the majority of the secreting vessels in insects, the testes are commonly slender and convoluted, and they occupy nearly the same portion of the abdomen as the ovaries in the opposite sex. ”

“ To deposit her eggs, the female bores with her ovipositor into the stems of plants, the tissues of animals, or the timbers of our houses. There are no old tree-trunks or cracked walls that may not serve her for a hatching place. The female takes care to place her eggs in conditions which will permit her progeny to find food for themselves from birth ”

“ CHAPTER III. ELASMOBRANCHII. The impregnation of the ovum is effected in the oviduct. In most forms the whole of the subsequent development, till the time when the embryo is capable of leading a free existence, takes place in the uterus; but in other cases the egg becomes enveloped, during its passage down the oviduct, first in a layer of fluid albumen, and finally in a dense horny layer, which usually takes the form of a quadrilateral capsule with characters varying according to the species. ”

“ It has been possible to prove that the mere presence of an anatomically normal reproductive system, including a normal ovary with a full complement of ova, and a normal
oviduct, is not enough to insure that a hen shall lay eggs, that is, exhibit actual as well as potential fecundity. While comparatively very rare, cases do occur in which a bird possesses a perfect ovary and perfect oviduct and is in all other respects entirely normal and healthy, yet never lays even a single egg in her life time. ”

“ The spermatozoa do not attain maturity until they reach the uterus of the female.
The internal female reproductive organs are, with few exceptions (Trichina, etc.) , double, but the vagina, which is lined with cuticle continuous with that covering the body, is always single. They are usually much coiled, and may be divided into ovary, oviduct, and uterus. The ova arise from a polynucleated mass of protoplasm or syncytium (Fig. 65, o) at the upper end, and acquire distinctness as they approach the oviduct. ”

“ The ovaries always contain spermatozoa, some of which project through the ovarian wall into the body cavity. Spermatozoa are not found in the uterus and oviducts, and it appears probable that they reach the ovary directly by boring through the skin and traversing the body cavity. [6] In the neotropical species there is a globular receptaculum seminis opening by two short ducts close together into the oviduct, and there is a small receptaculum ovorum with extremely thin walls opening into the oviduct by a short duct just in front of the receptaculum seminis. ”

“ This true ovary is somewhat lateral in most Rotifers, but is median in Asplanchnidae, and paired in Pterodina, Bdelloida, and Seisonaceae. A membranous covering is common to the ovary and yolk-gland (paired when these are paired) ; it is continued into a thin-walled tube or oviduct, which opens into the cloaca on its ventral side beyond the bladder or common renal duct. In the viviparous species the mature ovum (Fig. 112, em) usually lies in the oviduct, dilating it into a sort of "uterus" until the birth of the young. ”

“ The ovum from which this embryo takes its origin is visible long before the separate Salps of the chain have become completely developed. It is enveloped in a capsule continuous with a duct, which opens into the atrial cavity, and is usually spoken of as the oviduct. The capsule with the ovum is enveloped in a maternal blood sinus. Embryonic development commences after the chain has become broken up, and the spermatozoa derived from another individual would seem to be introduced to the ovum through the oviduct. ”

“ The fertilization of the female takes place once for all a long time previous to oviposition; the semen in the receptaculum seminis passes out as the eggs slip down the egg-passage, and a spermatozoön gains entrance into the interior of the egg through the micropyle. In Œcanthus, according to Ayers, fecundation probably takes place while the egg is passing into the vagina, “since it is hardly possible that the male element could gain access to the follicles before the chorion is secreted.” ”

“ The ovary is median. In young females it is of an elongated oval shape; in older females the posterior end becomes club-shaped, whereas the anterior end becomes attenuated; the oviduct originates at the posterior end, but immediately turns forwards and joins the parallel vitelline duct in front of the ovary (fig. 174) , where the shell gland cells open; the common canal becomes dilated to form the oötype, and then proceeds as the uterus, with only slight convolutions, along the central field to the genital pore, which lies in the middle line immediately behind the ventral sucker. ”

“ Reproductive System.—All the Hexapoda are of separate sexes. The ovaries (fig. 13) in the female are paired, each ovary consisting of a variable number of tubes (one in the bristle-tail Campodea and fifteen hundred in a queen termite) in which the eggs are developed. From each ovary an oviduct (fig. 13, od) leads, and in some of the more primitive insects (bristle-tails, earwigs, may-flies) the two oviducts open separately direct to the exterior. Usually they open into a median vagina, formed by an ectodermal inpushing and lined with chitin. ”

“ The queen, it will be remembered, cohabits with the male but once in her life. The sperm-cells then received are stored in a special receptacle and are released during the passage of the egg down the oviduct. In this act of releasing the fertilizing germs a singular economy is practised. In the case of most other creatures myriads of sperm-cells are released for the fertilization of a single egg, and of these but one can possibly attain its goal, the minute aperture or “micropyle” which is the doorway to the germ liberated, in the form of an egg, by the female. The rest die. ”

“ The uncertainty becomes still greater owing to our inadequate knowledge as to the length of time during which the sexual elements, the ova and the spermatozoa, retain their vitality after liberation from their respective sources. While it is not certainly known, it is probable that the ovum is capable of impregnation any time during its sojourn within the oviduct and before reaching the uterus, or probably for a period of about one week from the time of its escape from the Graafian follicle. ”

“ The difference is this: true parthenogenesis takes place in perfect females, capable of sexual union and of fertilization, possessing perfect ovaries and producing true ovules which develop into embryos without fertilization. The larval aphid, on the contrary, is not a perfect female, is not capable of sexual union nor of fertilization; its ovary-like organ is not a true ovary, does not produce true ovules which develop into embryos, but forms an embryo at once within, which then is born in an active state. ”

“ Posteriorly they end in two short oviducts which open into a uterus, in which fertilisation takes place, and in which the secretion arises which cements the eggs together. In the adult the ovaries and a receptaculum seminis are found, in addition to the organs present in the larva. The ovaries are formed from modifications of the packing tissue; they begin close behind the head, and soon attain such dimensions as to compress the egg-sacs and body-cavity to small slits. ”

“ The undeveloped ovary of an adult female Grouse would about cover a threepenny piece, but is long and triangular in shape rather than circular. The oviduct in a breeding hen is a large and conspicuous duct, and may, of course, contain an egg with the shell in course of formation, being pigmented in preparation for laying. The oviduct in a barren bird, or in a hen at other times than the breeding season, is a very much less conspicuous object, and is less easily found than the small and undeveloped ovary. ”