320 MAGNALIA NATURE: OR THE GREATER 



ing to this angle, the second chamber may happen to be 

 all but detached (Globigerina), or, with all intermediate 

 degrees, may very nearly wholly enwrap the first. Take 

 any specific angle of contact, and presume the same condi- 

 tions to be maintained, and therefore the same angle to be 

 repeated as each successive chamber follows on the one 

 before ; and you will thereby build up regular forms, spiral 

 or alternate, that correspond with marvellous accuracy to 

 the actual forms of the foraminifera. And this case is all 

 the more interesting, because the allied and successive forms 

 so obtained differ only in degree, in the magnitude of a single 

 physical or mathematical factor ; in other words, we get not 

 only individual phenomena, but lines of apparent orthogenesis, 

 that seem explicable by physical laws, and attributable to 

 the continuity between successive states in the continuous 

 or gradual variation of a physical condition. The resem- 

 blance between allied and related forms, as Hartmann 

 demonstrated, and Giard admitted years ago, is not always, 

 however often, to be explained by common descent and 

 parentage. 1 



In the segmenting egg we have the simpler phenomenon 

 of a laminar system, uncomplicated by the presence of a 

 solid framework ; and here, in the earliest stages of segmen- 

 tation, 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, these 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. 



1 Cf. Giard, ' Discours inaugurate,' Bull. Scientif., iii. p. 1, 1888. 



