402 TRANSACTIONS OB' SECTION D. 



ago, is not always, however often, to be explained by common descent and 

 parentage. 6 



In the segmenting egg we have the simpler phenomenon of a 'laminar system,' 

 uncomplicated by the presence of a solid frame- work ; and here, in the earliest 

 stages of segmentation, it is easy to see the correspondence of the planes of 

 division with what the laws of surface-tension demand. For instance, it is not 

 the case (though the elementary books often represent it so) that when the totally 

 segmenting egg has divided into four segments, the four partition walls ever 

 remain in contact at a single point ; the arrangement would be unstable, and the 

 position untenable. But the laws of surface-tension are at once seen to be 

 obeyed, when we recognise the little cross-furrow that separates the blastomeres, 

 two and two, leaving in each case three only to meet at a point in our diagram, 

 which point is in reality a section of a ridge or crest. 



Very few have tried, and one or two (I know) have tried and not succeeded, 

 to trace the action and the effects of surface-tension in the case of a highly com- 

 plicated, multi-segmented egg. But it is not surprising if the difficulties which 

 such a case presents appear to be formidable. Even the conformation of the 

 interior of a soap-froth, though absolutely conditioned by surface-tension, pre- 

 sents great difficulties, and it was only in the last years of Lord Kelvin's life 

 that he showed all previous workers to have been in error regarding the form of 

 the interior cells. 



But what, for us, does all this amount to ? It at least suggests the possibility 

 of so far supporting the observed facts of organic form on mathematical prin- 

 ciples, as to bring morphology within or very near to Kant's demand that a true 

 natural science should be justified by its relation to mathematics. 7 But if we 

 were to carry these principles further and to succeed in proving them applicable 

 in detail, even to the showing that the manifold segmentation of the egg was but 

 an exquisite froth, would it wholly revolutionise our biological ideas? It would 

 greatly modify some of them, and some of the most cherished ideas of the 

 majority of embryologists ; but I think that the way is already paved for some 

 such modification. When Loeb and others have shown us that half, or even a 

 small portion of an egg, or a single one of its many blastomeres, can give rise 

 to an entire embryo, and that in some cases any part of the ovum can originate 

 any part of the organism, surely our eyes are turned to the energies inherent in 

 the matter of the egg (not to speak of a presiding entelechy), and away from 

 its original formal operations of division. Sedgwick has told us for many years 

 that we look too much to the individuality of the individual cell, and that the 

 organism, at least in the embryonic body, is a continuous syncytium. Hof- 

 meister and Sachs have repeatedly told us that in the plant, the growth of the 

 mass, the growth of the organ, is the primary fact; and De Bary has summed 

 up the matter in his aphorism, Die Pflanze bildet Zcllen, nicht die Zelle bildet 

 l J flanzen. And in many other ways, as many of you are well aware, the extreme 

 position of the cell-theory, that the cells are the ultimate individuals, and that 

 the organism is but a colony of quasi-independent cells, has of late years been 

 called in question. 



There are no problems connected with Morphology that appeal so closely to 

 my mind, or to my temperament, as those that are related to mechanical con- 

 siderations, to mathematical laws, or to physical and chemical processes. 



T love to think of the logarithmic spiral that is engraven over the grave of 

 that great anatomist, John Goodsir (as it was over that of the greatest of the 

 Bernouillis), so graven because it interprets the form of every molluscan shell, 

 of tusk and horn and claw, and many another organic form besides. I like to 

 dwell upon those lines of mechanical stress and strain in a bone that give it 

 its strength where strength is required, that Hermann Meyer and J. Wolff 

 described, and on which Roux has bestowed some of his most thoughtful work ; 



Cf. Giard, ' Discours inaugurale,' Bull. Scientif. (3), 1, 1888. 



7 ' Ich behaupte aber dass in jeder besonderen Naturlehre so viel eigent- 

 liche Wissenschaft angetroffen weiden konne, als darin Mathematik anzutreft'en 

 ist.' — Kant, in Preface to Metaphys. Anfangsgriinde der Naturwissenschaft 

 ( Werhe, ed. Hartenstein, vol. iv., p. 360). • 



