Oviposition

“ It should be remembered that the ovipositor is really composed of several appendages that are developed from the outside of the body; thus the external orifice of the body is morphologically at the base of the borer, the several parts of which are in longitudinal apposition. Hence there is nothing that would render the view of the egg leaving the ovipositor at the base improbable, and Adler supposes that it actually does so, the thin end being retained between the divisions of the terebra. Riley is of opinion that the act of oviposition in these Insects follows no uniform system. ”

“ After oviposition, which may extend over several weeks, the female dies. The newly-hatched young has only three pairs of legs and is without spiracular and genital orifices. These young, or larvae as they are called, after the integument has hardened by exposure to the air, climb up the stalks of grain or herbage and cling with outstretched legs waiting for passing animals. They seize hold of the first that brushes by, and crawling to a suitable place become engorged with blood. ”

“ The male and female frequently work together at the task of preparing the nest. When oviposition is about to take place, the male may be seen to suddenly attach himself to the dorsal surface of the head of the female which holds on to one of the stones at the upper margin of the nest. The urogenital opening of the male, with its specially prominent papilla, is approximated to that of the female, and with a peculiar quivering movement the eggs and sperms are emitted synchronously amidst clouds of sand stirred up by the movements of the tail. ”

“ 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.” ”

“ He concludes, with reason, that the access of the impregnating fluid contained in the receptacle is cut off at pleasure by an instinctive act of the female in oviposition. The workerbees,or females with undeveloped organs of generation, being incapable of impregnation, in the rare cases in which their ovaries are sufficiently developed to mature a few eggs, these produce only male brood.We have not space to do more than allude to various other interesting topics which Siebold has linked to these inquiries ”

“ As she increases in dimensions, they continue to enlarge the cell in which she is detained. When the business of oviposition commences, they take the eggs from her, and deposit them in their nurseries. Her abdomen now begins gradually to extend, till in process of time it is enlarged to fifteen hundred or two thousand times the size of the rest of her body, and her bulk equals that of twenty or thirty thousand workers. ”

“ No eggs are deposited until the foliage is well along usually, as this is the food of the larvae. The writer observed a female during oviposition. She thrusts out the egg and by a mucilagenous substance causes the egg to adhere fast to the leaf. She decorates the egg, as it were, with a fluid which later turns black and appears as a streak across the ova. The adults do not live long after egg deposition, usually about a week and a half. A number of females were observed to lay from forty to fifty eggs each. ”

“ After oviposition the male remains on guard until the young are hatched out, when they appear to leave the nest in a body, still under the protection of their watchful parent. At all events a little later the male has been observed to be accompanied by a swarm of young fry, which he keeps together by circling round them. The development of the eggs is remarkably rapid. From the first cleavage of the egg to the hatching of the embryo the whole {501}process may be completed within from 4 to 8 days. ”

“ The internal organs of reproduction in the female consist of the ovaries, from which the eggs pass by way of the oviduct to the ovipositor, which in butterflies is not so conspicuous or remarkable an organ as is the case in many other insects. Communicating with the oviduct are the spermatothecæ, which are receptacles in which is retained the fertilizing fluid received from the male at the time of coition. As the eggs, one by one, are passed from the ovaries into the oviduct, they are impregnated through absorption of the spermatozoa, which enter their walls, imparting to them vitality. ”

“ 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. ”

“ 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. ”

“ Ovipositor.—If the specimen is a female, it has an egg-placer or ovipositor, consisting of four blunt projections at the end of the abdomen (Fig. 107) . If it is a male, there are two appendages above the end of the abdomen, and smaller than the parts of the ovipositor. Females are larger and more abundant than males. In laying the eggs, the four blunt points are brought tightly together and then forced into the ground and opened (Fig. 108) . By repeating this, the grasshopper makes a pit almost as deep as the abdomen is long. The eggs are laid in the bottom of the pit. ”

“ 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. ”

“ 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 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 ”

“ Some hours or even a day before the laying, that egg by itself represents or even exceeds in bulk the whole of the ovigenous apparatus. This is the egg which is on the point of being laid. It is about to descend into the oviduct, in its proper order, at its proper time; and the mother has no power to make another take its place. It is this egg, necessarily this egg and no other, that will presently be laid upon the provisions, whether these be a mess of honey or a live prey; it alone is ripe, it alone is at the entrance to the oviduct ”

“ All alike are generated from sexual union, the male emitting semen into the female. But among the ovipara (1) birds produce a perfect hard-shelled egg, unless it be injured by disease, and the eggs of birds are all two-coloured. (2) The cartilaginous fishes, as has been often said already, are oviparous internally but produce the young alive, the egg changing previously from one part of the uterus to another; and their egg is soft-shelled and of one colour. One of this class alone does not produce the young from the egg within itself, the so-called ‘frog’ ”

“ 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 eggs contain much yolk, and, like those of the fowl, are very large; like the fowl, too, one of the ovaries is suppressed, and it is the right ovary that alone remains. The two oviducts meet in front of the liver ventral to the oesophagus, and have there a common opening by which the ova are received after being shed into the body cavity. The eggs receive an oblong horny case in the oviduct; in the figure such a case is figured as distending the duct at e. The testes of the male (T. in Figure 2) are partially confluent in the middle line. ”

“ 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. ”

“ Here the egg remains a certain length of time, and then if it is not fertilized it is passed away; but if it is fertilized a marvellous change takes place in this tiny cell: it remains within the oviduct and is there supplied with nourishment by blood-vessels essentially as the flower seed is supplied with food from the sap. Generally three or five of these ova develop at the same time, some in one oviduct, some in the other. When these tiny eggs have developed into kittens [Pg 157] strong enough and perfect enough to make entrance into the world safe, they are born just as the egg is born. ”

“ 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. ”

“ It is only when they get into a fluid medium that they show the power of undulatory movement, feeble at first, but gradually more energetic and more violent. And these movements enable them to penetrate like gimlets into the calcareous egg-shell. In the normal course it happens that when a mature ovum is deposited from the opening of the oviduct, one of the giant zoosperms at the same time, or shortly afterwards, leaves the 'receptaculum seminis' of the female by way of the spiral passage, and reaches the exterior just behind the ovum. ”

“ The bird strains violently but ineffectually and rubs its anus on the ground. The swelling goes on steadily and rapidly increasing, and the bird becomes more prostrate and hopeless. Sometimes the overdistended and congested oviduct gives way and the eggs escape into the abdomen. Reul has counted as many as 24 eggs that had thus escaped into the abdominal cavity. Or without rupture of the oviduct, the soft eggs pack together into a solid, dry yolk-like mass, the watery parts having been pressed out or absorbed. ”

“ This part is the rudiment of the oviduct proper, and forms a direct continuation of the above-mentioned cell-cord which is situated ventralward from the genital cells, from which, as we have seen, the proximal cup-shaped section of the oviduct is formed. The hinder section of the oviduct turns down ventrally in order to unite at the boundary between the 7th and 8th abdominal segments with the hypodermis. The rudiment of the oviduct originally forms a solid strand of cells. Afterwards a cavity is formed by the separation of the cells. ”

“ 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. ”