Oct. lo, 1 872 J 



NATURE 



483 



S IE B OLD'S NEW RESEARCHES IN 



PARTHENOGENESIS * 



A MIDST the all-absorbing discussion of the problems which 

 -^ *- have arisen out of the general acceptance among biologists 

 of the law of evolution, the phenomenon of Parthenogenesis 

 which, previously to Mr. Darwin's work on the Origin of Species, 

 excited the interest and called forth the investigations of observers 

 in much the same manner as his theory has done of late years, 

 has met with a reverse of fortune and fallen into a subordinate 

 rank of popularity. The distinguished naturalist, however, who 

 fifteen years ago gave so stunning a blow to current theories of 

 the reproductive process, by demonstrating the occurrence in 

 moths and bees of what he designated as ' ' true parthenogenesis " 

 — that is to say, the development, without impregnation, of an 

 ovum capable of being impregnated — has not let the subject drop. 

 I'rofessor Siebold has made further experimental researches, 

 establishing again, and on a larger basis, his former conclusion, 

 and ackling at least one new fact of great general importance for 

 the understanding of the process of sexual reproduction. Although 

 upon its first appearance in 1S56, the conclusion arrived at in his 

 " VVahre Parthenogenesis " was admitted by almost all compe- 

 tent naturalists to be thoroughly demonstrated, and beyond the 

 reach of criticism ; yet some more and some less eminent biolo- 

 gists have not been wanting to deny the Liicina sine lOiicnbitii, 

 and have raised such objections as that of a possible error in the 

 condition of the experiments depending on the exclusion of males 

 from the supposed parthenogenetic female ; and again, that these 

 so-called females were not demonstrated "not to be hermapliro- 

 dites." Indeed so deeply rooted is the conviction that eggs are 

 made to be impregnated by spermatozoa, and that they then, and 

 then only, can proceed to develop, that Siebold felt it necessary to 

 add to his proofs, in order to establish his position that not only 

 do unimpregnated eggs develop into perfect animals, but that 

 such an event is by no means an exceptional occurrence among 

 certain groups, and has a definitely fixed and orderly recurrence 

 amongst them. He naturally was also anxious to extend the 

 class-limits within which a true parthenogenesis can be said to 

 occur, and he desired to inquire into the sex of the parthenoge- 

 netically-produced offspring in such cases as could be critically 

 and decisively studied. Hence the renewed researches which 

 have extended over several years, and the results of which are 

 given in the present brochure. 



Von Siebold's merit in this and his former work (but more 

 especially in this) is not the enunciation of a new theory, or hypo- 

 thesis, but the great care, ingenuity, and persistence which he has 

 displayed in investigating cases in which for many years collectors, 

 bee-keepers, and such naturalists of the limited, or "gardener" 

 type, had asserted reproduction by means of unfertilised eggs to 

 take place. It must be remembered that he was himself a strong 

 opponent in 1S50 of the supposition which he has now shown to 

 be justified in fact, and thatLeuckart in his article "Zeugniss," in 

 Wagner's Handwiirterbuch, and in other publications, preceded 

 him as an advocate for the existence of true parthenogenesis, en- 

 deavouring, by microscopical researches, to give a solid observa- 

 tional basis to Dzierzon's hypothesis. It was not until 1S57 that 

 Siebold published his observations on bees, demonstrating what 

 had been previously supposed, viz., that the queen-bee exhausts her 

 store of received sperm in fertilising eggs which give rise to females 

 only, and that then she lays unfertilised eggs, which become drones 

 only, whilst the unfertilised worker-females also lay eggs which 

 give rise to drones, and again that in certain moths {Psyche and 

 Solciiolna) unfertilised ova develop and produce females only. 

 Leuckart followed (1S58) with his " Zur Kenntniss des Genera- 

 tions-wechsels und der Parthenogenesis bei den Insekten." In 

 this work, whilst asserting his clamis to the merit of first espousing 

 the cause of true parthenogenesis, Leuckart gives an excellent 

 view of the general signification of the phenomena, and insists 

 on the importance of extended histological observation in the ex- 

 amination of alleged cases of parthenogenesis. In his present 

 work Siebold cannot be charged with in any way neglecting this 

 part of his subject, for he has given most important and minute 

 descriptions of the generative organs of the two principal cases 

 studied {Polistcs and Apiis), containing new facts. His method is 

 however eminently experimental, and appears to us a striking 

 contradiction of a very superficial classification of the sciences, 

 which is favoured sometimes by men of science unacquainted 



* " Beitragc zur r.irlhenogenc5is der Arthropodeu." Von C. Tli. E. von 

 Siebold, Professor der Zoologie und Vergleichenden Aiiatomie in Miinchcn. 

 Leipzig : Engelmann, 1871.) 



with the methods or problems of biology : we mean the division 

 into the exact or mathematical, the experimental, and the classi- 

 ficatory sciences, in which last division the so-called natural 

 history sciences are said to find their place. 



The experiments which Siebold made on bees and wasps, 

 though performed by a naturalist, are as nicely controlled, and 

 as clear in the conclusions which they give, as any performed by 

 exact physicists on the times or quantities concerned in this or 

 that physical process. The style in which details of these in- 

 vestigations are communicated is one rare at the present day in 

 biological works, where minute description of structure, or of the 

 apparatus devised for a physiological research, form the staple. 

 Plere we are treated to a leisurely narrative of some years of 

 patient work ; we share the keen enjoyment of the author as he 

 becomes acquainted with the marvellous intelligence of his wasps 

 and their various proceedings —we feel his satisfaction in over- 

 coming the difficulties of procuring and observing the necessary 

 material, and admire the candour and thoroughness with which 

 he handles the question before him. 



Before proceeding to a short notice of the contents of Von 

 Siebold's book, it will be well to give a brief statement of the 

 signification which such inquiries as his have in the present state 

 of knowledge. Harvey's dictum, "Omne vivum ex ovo," ex- 

 pressed a great law, which had to be qualified when the researches 

 of Trembley and others made known, among Polyps, and Worms, 

 and Protozoa, reproduction by fission. To this rapidly succeeded 

 the recognition of a modified fission, in which the animal did not 

 divide into equal parts, nor exhibit the power of reproduction of 

 the whole animal in artificially detached portions of its body ; 

 but in which special sprouts or buds were found to be prepared 

 and detached spontaneously, becoming then developed into per- 

 fect animals. This process received the name of gemmation, 

 and was stated to occur in polyps and also in the plant-lice. 

 Parallels for these methods of reproduction in animals were 

 readily recognised in plants, in the multiplication by seed, by 

 cuttings or shoots, and by separable buds. A broad line was 

 drawn between " buds " and "eggs," however egg-like the for- 

 mer might appear, in the assumption that eggs were special 

 bodies of a peculiar structure, destined to be "fertilised" by the 

 spermatozoa of the male — after which process only could they 

 develop. These distinctions, some twenty years ago, were the 

 more firmly impressed in the minds of biologists by the then re- 

 cently acquired knowledge of the process of fertilisation or im- 

 pregnation. Then came the demonstration by Siebold of the 

 capacity for development of true eggs, even when not impreg- 

 nated. The sharpness of the limit between buds and eggs was 

 by this at once destroyed ; and the closely following researches 

 of Leydig (antecedent to Siebold's work in some cases), Ilu.xley, 

 Lubbock, and Leuckart, on the structure of the supposed buds 

 of Aphis and allied insects, and of lower crustaceans, proved 

 that these bodies were morphologically ova — originating in 

 ovaries, and having the essential structure of fertihsable ova. 

 For them the term "pseudova" was introduced by Prof Hux- 

 ley, since they differ in this respect from other ova — that whereas 

 the latter can be, and are in most cases (though with constant 

 exceptions), fertilised, the latter cannot be.* Whilst, then, up to 

 this period such a thing as parthenogenesis appeared to be a strange 

 exception, the question has now shifted, and, since the essential 

 identity in reproductive power of cuttings, buds, pseudova, and 

 eggs is proved, the problem before naturalists is rather, "Why 

 are eggs ever fertilised?" in short, "What is the use of the 

 male sex at all ? " We have animals and plants multiplying by 

 fission, breaking up into two or more parts, each of which be- 

 comes a new individual ; we have them giving rise by growth to 

 masses of cells, which become detached or remain attached, and 

 develop each into a new individual ; and finally, we have them 

 elaborating single large cells, which become detached and deve- 

 lop each into a new individual. Why should it be that in certain 

 cases these last require the fusion of another peculiar kind of 

 cell elements before they will develop ? Some light seemed to 

 be thrown on this matter at first, by the observation that the 

 unfertilised ova of the bee always produce drones, and that only 

 the fertihsed produce females ; but this indication of a possibly 

 .clearer insight into the matter is entirely upset by the fact, now 

 fully established in the present work, that in some species of 



* Leuckart has more recently proposed, in describing the reproduction of 

 the Cecidomyia larva discovered by Wagner, to limit the term " pseudovum" 

 to such ova as those produced by larva;, or imperfect forms ; and not to apply 

 it at all to the eggs of bees, wasps, &c. (which can develop without fertilisa- 

 tion), as was done by Huxley. The falsity implied in the prefix seems to 

 make a rather stronger distinction than is desirable between any of these 

 bodies ; for they are all truly ova, though ova of various special properties. 



