PARTHENOGEN'ESTS (ante). 'This term, as employed by prof. Owen and applied, as noticed in the preceding article, to the processes of gemination and fission as exhibited in sexless beings or virgin females, is not strictly the generative process which is now indicated by its use. The term is now confined to the generation of new individuals from the development of ova by virgin females without contact with the male element. The peculiarity of this process is appreciated by regarding the proper definition of an ovum, and its distinction from an internal bud. An ovum is usually contained in an ovary, and always has a germinal vesicle and a germinal spot, and during its develop ment undergoes what is known as segmentation of the yelk. Examples of true partheno genesis are seen in certain plant-lice (aphides), the honey-lmT, and sonic of the lower and smaller crustaceans, as now classified. In the autumn, plant-lice consist of males and females, which'by sexual union produce ova; but these remain dormant during the win ter. In the spring they-are hatched, but, instead of producing males and females, the young are all of one kind, variously regarded as neuters;Temales, or hermaphrinlites. These oviparous products, whatever their nature may be, now produce viviparously a brood of young resembling themselves, these in turn bringing forth a third generation; and the same viviparous process may be repeated a considerable number of times during the summer. The last generation, however, brought forth at the commencement of autumn will not be all of one kind, but will consist of distinct sexes. Now sexual repro duction by means of eggs takes place, as in the preceding autumn, to be followed in the spring by another series of viviparous generations. The viviparous multiplication of the aphides is multitudinous, and it has been estimated that ten generations of a single aphis during one summer may reach the number of one quintillion. The ovary of each vivip arous aphis resembles that of a fertile female, with certain exceptions which cannot well be described here. It may be regarded as a pseudo-ovary, and it generates or develops
eggs or "pseudo-ova," which, without male intervention, are developed into young aphides. There is no anatomical difference between the pseudo-ova and true ova, the distinction being purely physiological. Some naturalists, however, maintain that the viviparous aphides are hermaphrodites, possessing both sexual elements, in which caso their mode of generation would not be an example of partbencmenesis; but this view is not entertained by most observers. In regard to certain reproductive phenomena among honey-bees there seems to be but little doubt. There are three classes of individuals in is hive of bees; a queen, or fertile female; workers, forming the bulk of the community and which are examples of arrested development in females; and, thirdly, the drones, or main bees, produced at certain times of the year. The wonderful impregnation of the queen, which occurs during her "nuptial flight," results in the storing up of fecundating material in a receptacle which communicates by a tube with the oviducts, and which material, it is said, can be used at will, or at least is used periodically, as occasion requires. The ova which become undeveloped females, or workers, are fertilized during their passage through the oviduct; and the subsequent development of these fecundated ova into queens or into workers, as the case may require, depends upon the form (seem ingly) of the cell which receives the ovum, and upon the food which is given to the larva. There is nothing in the evidence so far produced to show non-sexual generation; but careful observers have succeeded—by preventing, as they assert, the contents of the seminal receptacle of the queen from passing into the oviduct, and thus coming into con tact with the ovum—in causing her to produce none but males, or drones. If these observers are correct, this case is one of parthenogenesis; and at present the prevailing tendency is toward the acceptance of their conclusions.