I 



April 5, 1900] 



NATURE 



551 



the campaign against plague, one expects to find some radical 

 alteration advised ; but no, they turn round and join forces, 

 saying, " We recognise that even though a vaccine which is in- 

 sufficient.y standardised, and which is occasionally contaminated, 

 is from the scientific point of view a very imperfect vaccine, yet 

 judged from the standpoint of practical life, such defects may 

 very well be overlooked if the insufficient standardisation and the 

 occasional contamination of the vaccine have not interfered in a 

 sensible manner with its utility. 



" This standpoint, which is indeed the only reasonable stand- 

 point, is the standpoint which has been taken up by Mr. Haff^kine 

 in the statement that was handed in by him, and which is pub- 

 lished, at his request, in our Proceedings." 



The second part of the report criticises the statistics of anti- 

 plague inoculations. In their summary, the Commissioners say 

 that inoculation diminishes the number of attacks and diminishes 

 the death-rate among those inoculated, that it does not appear to 

 confer any degree of immunity till a few days have elapsed after 

 inoculation, and that the protection lasts certainly for a consider- 

 able number of weeks, and possibly for some months. 



They recommend that inoculations under safeguards and con- 

 ditions stated in the report should be encouraged wherever 

 possible, and in particular among disinfecting staffs and attendants 

 of plague hospitals. C B S. 



EXPERIMENTAL STUDY OF 

 FERTILISATION. 



TN 1898 Prof. Yves Delage made a remarkable experiment. ^ 

 -'■ He divided the unfertilised 'egg of a sea-urchin {Strongy- 

 loceiilrotus lividus) under the microscope into two parts — one 

 containing the nucleus and the centrosome, the other simply 

 cytoplasmic. Beside these he placed an intact ovum, and then 

 supplied spermatozoa. Towards these the three objects showed 

 equal "sexual attraction"; all three were fertilised; and all 

 three segmented, the intact ovum most rapidly, the nucleated 

 fragment more slowly, the non-nucleated fragment more slowly 

 still. In one experiment, the development proceeded for three 

 days, during which the intact ovum had become a typical gas- 

 trula, the nucleated fragment a smaller gastrula, and the non- 

 nucleated fragment a quasi-gastrula with almost no cavity. In 

 each case the cells showed nuclei. The conclusion was then 

 drawn that fertilisation and some measure of development may 

 occur in a fragment of oz'um without nucleus or ovocentre, and 

 it was suggested that we have in fertilisation to distinguish two 

 processes : — (a) the stimulus given to the ovum by a specially 

 energetic kinoplasm brought in by the spermatozoon, perhaps 

 in its centrosome ; and {b) the mingling of heritable qualities, or 

 amphimixis. One may also note that the experiment was sug- 

 gestive in furnishing experimental confirmation of what is 

 generally assumed, that each of the sex-cells is a fully equipped 

 potential individuality. Here we may recall the remarkable ex- 

 periment of H. E. Ziegler,*-* who divided the just fertilised ovum 

 of a sea-urchin in such a way that each half had one pronucleus, 

 and observed that the half with the male pronucleus seg.nented 

 and formed a blastula. 



In 1899 Delage continued his experiments,' and with striking 

 success. Non-nucleated fragments of the ova of a species of 

 Echinus, of Dentalium entale, and of Lattice conchilega were 

 effectively fertilised ; they proceeded to develop, and gave rise to 

 plutei, veligers, and trochophores respectively. The terms 

 merogonic fertilisation and merogonic development are suggested 

 to express the remarkable facts observed. 



The segmentation of the fertilised non-nucleated fragment was 

 practically normal in the sea-urchin, very irregular in Dentalium, 

 less irregular in Lanice (the chief irregularity being lack of 

 correspondence between the nuclear and the cytoplasmic 

 divisions), but as the development proceeded some self-regu- 

 lative process reduced the abnormalities to insignificance. The 

 plutei only differed from the normal in the extreme reduction of 

 the arms ; the veligers and trochophores were almost typical. 

 They showed no lack of vitality, and although further develop- 

 ment did not occur, the same is usually true of normal larvae 

 reared in similar conditions. 



1 " Embryons sans noyau maternel." C. K. Ac. Set. Paris, cxxvii. 

 (i8p8), pp. 528-531. 



- "Arch. Entwickelungsmechanik,'' iv. (1898), pp. 249-293, 2 plates, 3 

 figs. 



3 "fetudessurla merogonie." Arch. Zool. expfr, ■v'\\. (1899), PP- 383- 

 417, II figs. See also C. R. Ac. Sci. Paris, Cxxix. (1899), pp. 645-648. 



NO. 1588, VOL. 61] 



As to the limits of possible mero^ny, Delage got some results 

 which are nothing if not striking. A quarter of a Dentalium- 

 ovum was fertilised and segmented ; about a fifth of a Lanice- 

 ovum was successfully treated ; but the chef d'aiivre of 

 experimental nicety was seen when 1/37 of a sea-urchin oz<um 

 ga7'e rise to an agile Has tula. Delage has christened his pigmy 

 creations — tetartogonic, pemptogonic, &c. — but he seems to 

 hesitate in regard to that arising from the 1/37, for he puts the 

 title " triacosthedomogonique " in a footnote. That there is a 

 limit to merogony he is convinced, but he will not at present fi.t 

 it. It seems not inappropriate to recall Marchal's description ^ 

 of the strange behaviour of the ovum o\ Encyrtus fuscicollis (one 

 of the parasitic Hymenoptera), which gives rise to a legion of 

 morulae, and forms a chain of 50-10x3 embyros within one 

 elongated amniotic envelope. For practical purposes it is con- 

 venient to remember that, just as four lancelet embyros may be 

 got by shaking apart the first four blastomeres, so Delage by 

 cutting a sea-urchin ovum obtains three larv;^; from one egg. 



The issues involved in these experiments are so serious 

 (biologically) that one is naturally led to consider possible 

 criticisms, which Delage in his candid scientific spirit has him- 

 self suggested. It is difficult to refrain from the suspicion that 

 there may have been some mistake somewhere. The best 

 criticism would, of course, be to repeat the experiments ; but in 

 default of this, let us briefly consider with the author some of 

 the possibilities of error, (a) It may be suggested that the eggs 

 experimented with had been previously fertilised by stray 

 spermatozoa ; but Delage's experience has been that the 

 spermatozoa die 24-36 hours after liberation ; and the water in 

 which the eggs were placed had stood for three or four days in 

 a stone cistern. Moreover, only in one case was segmenta'ion 

 seen among the eggs from which those experimented upon were 

 taken, {b) It may be suggested that the segmentation of the 

 fertilised non-nucleated ovum-fragments was not genuine, but 

 a pathological fragmentation such as is occasionally observed 

 after mechanical or chemical stimulation ; but it must be 

 remembered that larvae were reared, and there were, of course, 

 control observations on non-fertilised fragments. (<) It may be 

 suggested that the nucleus was cut in the delicate operations, 

 so that each part had really a portion of nucleus as well as 

 cytoplasm. But it must be remembered that the nucleus is 

 very small and very mobile, and thus runs little chance of being 

 cut ; in the clear ova of the sea-urchin it was sometimes seen 

 after the operation in the larger part, only once in the smaller 

 part, never in both. In the other two cases {Dentalium and 

 Lanice) the opacity of the egg hides the nucleus. Perhaps the 

 best answer is, that in one experiment three embryos were got 

 from one ovum, and that fragments representing i/io and 1/37 

 of the total volume of the egg were also seen to segment. It 

 seems, however, possible still to retort that the operation broke 

 the nucleus and caused a distribution of nucleoplasm into the 

 various fragments before they were quite separated. 



What are the conditions of successful merogony ? Delage 

 failed with the ova of Ciona, Haliotis, Chiton, Sabellaria, &.C., 

 and he almost failed with those of Lanice until he learned the 

 particular "tour de main" in cutting them. The experiment 

 is not practicable except with eggs which are liberated separ- 

 ately before fertilisation. It usually fails if there is a shell. The 

 ova to be tried by other experimenters should be naked or with 

 a delicate glairy envelope, not too brittle, of firm consistence, 

 and not less than i/iomm. in diameter. In all Delage's experi- 

 ments there was a certain percentage of failure, due perhaps to 

 the inability of the fragments to recover from their wounds, or 

 to a diminution in the viscous substance which surrounds the 

 ovum and keeps its parts together. But, in spite of these 

 failures, the number of merogonic segmentations was generally 

 at least equal to, and sometimes greater than, the number of 

 segmentations among intact ova in similar conditions, — a 

 remarkable fact which leads Delage to the daring suggestion 

 that the absence of the female pronucleus may favour fertilis- 

 ation. " The female pronucleus is perhaps useful in securing 

 for the embryo the advantages of amphimixis, but it is not 

 useful in fertilisation nor necessary for the development of the 

 parts of the organism.'''' 



The preceding paragraphs give the gist of Delage's remark- 

 able experiments, but there are some less secure addenda which 

 deserve notice. He has shown the possibility of merogonic 

 hybridisation ; he observed phenomena which point to a 



1 C. R. Ac. Sci. Paris, cxxxvi. (1898), pp. 662-664. Ann. Nat. Hist. ii. 

 pp. 28-30. 



