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Rh in all essential particulars with the ordinary eggs of other animals. This, however, he denies to be true of the agamic eggs in the Aphidæ, Coccidæ, and Daphniidæ, in all of which he denies that any Purkinjean vesicle exists. In the "Philosophical Transactions" for 1857, however, I have clearly described and figured the Purkinjean vesicle, both in the agamic, or so-called summer eggs, and also in the ephippial, or, as they are called, the winter eggs, of Daphnia, In the "Linnean Transactions" for 1858, vol. xxii., part iii, Professor Huxley has given an excellent account of the agamic egg of Aphis, and has figured a cell, which is evidently the Purkinjean vesicle, with its macula; though with his usual caution he does not actually so call it, but merely says that it "corresponds with the germinal vesicle and spot of an ovum," and that "it is not distinguishable from a germinal vesicle." As regards Coccus, Prof. Leuckart and I independently described the Purkinjean vesicle and spot. And as regards most of the other insects in which agamic reproduction has been observed, the Purkinjean vesicle has been observed by Prof. Leuckart in Chermes and Psyche, and by me in Cynips. Moreover, it is arguing in the very narrowest of circles, to maintain—1stly, that the agamic eggs are buds, and not true eggs, because they contain no Purkinjean vesicle or spot; and 2ndly, that the vesicle and spot which they do contain are not a true Purkinjean vesicle and spot, because the reproductive body is a bud, and not an egg. We have, however, I think, a crucial case in the hive-bee, and some other Hymenoptera and Lepidoptera, in which the eggs are capable of developing either with or without impregnation—a fact which must surely convince even the most sceptical that, though as a matter of convenience it is desirable to adopt Prof. Huxley's name "pseudovum," there is no necessary distinction between a pseudovum and an ovum, or true egg.

Prof. Leydig does not, therefore, I think, express the present state of our knowledge, when he asserts that the agamic eggs of Daphnia, Coccus, and Aphis, possess no Purkinjean vesicle. It is, of course, open to Prof. Leydig to dispute the accuracy of the observations made by Leuckart, Huxley, and myself; but it is, I think, to be regretted that he should have referred only to his own previous and incorrect observations, and have ignored all which has since been written on the subject. Prof. Leydig is so eminent a naturalist, that if he still adheres to his old opinions, we should be much interested to know the reason why; but such a supposition seems scarcely reconcilable with other passages of his work. Thus, in the description of Dida crystallina (p. 100), he says—"Die Eier bilden sich vom spitzen, umgeknickten Ende her; dort sind die kleinsten Eikeime, bestehend aus dem Keimblaschen mit solidem Keimfleck, und einer hellen, das Keimblaschen einschliessenden