emy, Jourdan, Siebold and others. They all agree that while parthenogenesis is rare in this species, it does sometimes occur, and it is known that the parthenogenetic eggs give rise to fertile males and fertile females, which may unite sexually and thus produce fertile eggs. Dr. Kipp has reared another form, Smerinthus populi, from eggs fertilized by a male which hatched from a parthenogenetic egg, and laid by a female which had been reared in the same way.

In Bronn's Klassen und Ordnungen, Gaerstecker gives the following list of moths in which parthenogenesis has been observed, with the name of the observer. The list might be greatly enlarged by the addition of cases which have been recorded since its compilation, but it is sufficient for our purpose, which is simply to show that the fact has been verified repeatedly by many ob

servers.

Sphinx ligustri, once....

Treviranus.

Smerinthus populi, four times....Nordmann, Brown, Newnham,

Smerinthus ocellatus, once..

Kipp. .Johnston.

Euprepia caja, five times.... Brown, Lehocq, Robinson, Schlapp,

Euprepia villica, once................

Saturnia Polyphemus, twice..

Barthélemy.

...Stowell.

.Curtis, De Filippi.

Gastropacha pini, three times.. ..Scopoli, Suckrow, Lacordaire.

Although these cases make a long list, which might be greatly increased, they are still exceptional, for in all these species almost all the eggs fail to develop unless they are fertilized by a male; but in some other groups of insects parthenogenesis occurs more frequently, and seems to be perfectly normal. The most remarkable instances are those which occur in the social insects, such as the bees.

It is well known that a community of honey-bees consists of individuals of three kinds-the workers or rudimentary females, which are the most numerous; the perfect females or queens, of which only one is usually present in a hive; and the drones or males.

In the workers, or as they are sometimes falsely called the neuter bees, the female reproductive organs are very imperfectly developed: the vagina is so small that union. with a male is hardly possible, and the receptaculumseminis is very rudimentary, yet it is well known to all bee-cultivators that they do sometimes lay eggs which are capable of development, not only in the honey-bee but in other species also. Among the honey-bees such fertile workers are always found in a hive which has lost its queen, and they have been called "drone mothers," from the fact that their eggs produce only drones or males.

The queen-bee is the only member of the hive which unites sexually with the males, and her reproductive organs are very large and well developed, as contrasted with those of the worker. Her receptaculum-seminis is large enough to retain a sufficient supply of the male fluid to serve for fertilizing great numbers of eggs, and it is usually found to contain a considerable quantity. Sexual union takes place during flight, and queens with imperfect wings are never impregnated, and Siebold,

Leuckart, Berlepsch, and others have shown, by microscopic examination, that in such cases the receptaculumseminis is empty, and the queen is a virgin. In such cases, as well as in hives, where the receptaculum-seminis of the queen has been exhausted by old age, or has been removed, it is well known to bee-cultivators that only drones are produced, while eggs destined to give rise to females, to workers or perfect queens, are produced only by queens which have been impregnated and have some of the male fluid in the receptacle. This fact, considered in connection with the fact that the. eggs laid by workers produce only drones, indicates that the drone eggs laid by an impregnated queen are not fertilized; and Siebold has found active spermatozoa on newly laid worker-eggs, but has failed to find them on drone-eggs. We are, therefore, compelled to believe that the queen is able to lay both fertilized and parthenogenetic eggs. It is stated that when a queen of the common German variety is crossed with a drone of the Italian bee she produces hybrid workers, while her male offspring are all pure German bees.

In certain Lepidoptera, as in the bees, parthenogenesis seems to be normal, and it has been observed in Solenobia and Psyche by a great number of ancient and modern naturalists, including Schrank, Réaumer, Pallas, De Geer, Scriba, Speyer, Reutti, Siebold, Leuckart, Hofmann, and others. Their observations show-1st, that the wingless female is abundant and widely distributed at all seasons, while the winged males are seldom met with, and are found only in certain restricted localities; 2d, that there is only one form of female; those which unite with the male, as well as those who do not, have perfect reproductive organs which resemble those of other butterflies. Parthenogenesis is the rule, and the female

lay eggs as soon as they have passed through the pupa stage. These parthenogenetic eggs give rise only to females, and these may give rise to female descendants in the same way for an indefinite number of generations; 3d, in at least one species (Solenobia triquetrella), the eggs which are laid by impregnated females give rise to both sexes.

Dufur, Kessler, Hartig, Walsh, and many other naturalists have shown that certain female gall-wasps are parthenogenetic; within recent years Bassett and Adler have made most interesting observations upon these wasps. In 1873 Bassett showed (Canadian Entomologist, 1873-75, p. 91) that great numbers of male and female wasps escape in June from certain galls which are found in very great abundance on the leaves of an oak. Late in the summer the females lay their eggs in the leaves of the same oak, and give rise to galls, which, however, are of quite a different character from those in which the insects were born. Early in the following spring a brood of females hatch from these winter galls, and at once lay parthenogenetic eggs, which give rise to the summer galls, and hatch in June into males and females.

Bassett and Adler have extended these observations to a great number of species, and the following account is taken from a paper by the latter writer ("Ueber den Generationswechsel der Eichen-Gallwespen," von Dr. H. Adler, Zeit. f. Wiss. Zool., xxxv. 151), who has carried on a long series of the most painstaking experiments, using every precaution against error.

He reared a great number of small oak-trees under glass cases, and then, introducing the wasps, traced their whole life history, and he found that in many species there is a winter gall, which is produced in the fall by a

fertilized female, and which gives rise early in the spring to a brood of females without males. These at once lay their eggs and form summer galls, from which both sexes are born.

In all cases the parthenogenetic forms are so different from the sexual forms that they had previously been described as distinct species, and in most cases they had been placed in distinct genera.

The following example selected from Adler's paper will give an idea of the character of his experiments: Neuroterus lenticularis is a wasp which is born within a small round gall which appears in July on the lower surfaces of oak leaves. The galls continue to grow until the end of September, when the leaves drop off and fall to the ground. In the spring the insects escape, and all of them are females, with their ovaries full of eggs, and the male of this species was unknown previously to Adler's experiments. He gathered the fallen leaves, and rearing the wasps in isolated captivity found that, soon after the female is born, she pierces the leaf buds of the oak, and lays her eggs. Adler marked by pieces of thread all the buds which the insect was actually seen to pierce, and in a few days he found on the leaves which expanded from these buds a great number of minute young galls, which soon became large enough to show that they were very different from the winter gall in which the parent was born.

This new gall proved to be one with which entomologists had long been familiar, as the birthplace of what had always been regarded as a wasp of quite a different genus-Spathogaster baccarum. It is a soft green gall, punctated with red spots, and it grows entirely through the leaf, so that part is on the upper and part on the lower surface. The oak trees with these galls were kept