LEYDIG ON DAPHNIID^;. 23 



in all essential particulars with the ordinary eggs of other animals. 

 This, however, he denies to be true of the agamic eggs in the Aphidse, 

 Coccidae, and Daphniida?, 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 Trans- 

 actions" for 1858, vol. xxii., part ih\, 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. Leuckarfc* and If independently described 

 the Purkinjean vesicle and spot. And as regards most of the other 

 insects in which agamic reproduction has been observed, the Purkin- 

 jean vesicle has been observed by Prof. Leuckart in Chermes and Psyche, 

 and by me in Cynips.J Moreover, it is arguing in the very narrowest 

 of circles, to maintain — lstly, 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 e°-<?s 



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 observa- 

 tions, 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 crystaUina (p. 100), he 

 says — " Die Eier bilclen sich vom spitzen,' umgeknickten Ende her ; dort 

 sind die kleinsten Eikeime, bestehend aus dem Keimblaschen mit soli- 

 dem Keimfleck, und einer hellen, das Keimblaschen einschliessenden 



* TJntersuchungen zur Naturlehre, 1858. f " Phil. Trans.," 1858. 



X I have already pointed out that, as regards Coccus, Prof. Leydig appears to have 

 generally examined his specimens in dilute acetic acid. This destroys the Purkinjean 

 vesicle, and is, therefore, prohably, the cause of his mistake. 



