604 THE FORMS OF TISSUES [ch. 



question, whether in each particular organisin the conditions are 

 such as to lead to one particular arrangement being predominant, 

 characteristic, or even invariable. In short, is a particular arrange- 

 ment of cell-partitions to be looked upon (as the published figures 

 of the embryologist are apt to suggest) as a specific character, or at 

 least a constant or normal character, of the particular organism? 

 The answer to this question is a direct negative, but it is only in 

 the work of the most careful and accurate observers that we find 

 it revealed. Rauber (whom, we have more than once had occasion 

 to quote) was one of those embryologists who recorded just what 

 he saw, without prejudice or preconception; as Boerhaave said 

 of Swammerdam, quod vidit id asseruit. Now Rauber has put on 

 record a considerable number of variations in the arrangement of 

 the first eight cells, which form a discoid surface about the dorsal 

 (or "animal") pole of the frog's egg. In a certain number of 

 cases these figures are identical with one another in type, identical 

 (that is to say) save for slight differences in magnitude, relative 

 proportions, or orientation. But I have selected (Fig. 256) six 

 diagrammatic figures, which are all essentially different, and these 

 diagrams seem to me to bear intrinsic evidence of their accuracy: 

 the curvatures of the partition-walls and the angles at which 

 they meet agree closely with the requirements of theory, and when 

 they depart from theoretical symmetry they do so only to the 

 slight extent which we might expect in a material system*. 

 Of these six illustrations, two are exceptional. In Fig. 256, 5, 

 we observe that one of the eight cells is insular, and surrounded 

 by the other seven. This is a perfectly natural condition, and 

 represents, like the rest, a phase of partial or conditional equili- 

 brium; but it is not included in the series we are now considering, 

 which is restricted to the case of eight cells extending outwards 

 to a common boundary. The condition shewn in Fig. 256, 6, is 



* Such preconceptions as Rauber entertained were all in a direction likely to 

 lead him away from such phenomena as he has faithfully depicted. Rauber had 

 no idea whatsoever of the principles by which we are guided in this discussion, 

 nor does he introduce at all the analogy of surface-tension, or any other purely 

 physical concept; but he was deeply under the influence of Sachs's rule of 

 rectangular intersection, and he was accordingly disposed to look upon the 

 configuration represented above in Fig. 256, 6, as the most typical or primitive. 

 His articles on Thier und Pflanze, in Biol. Cbt. iv, 1881, tell us much about this and 

 other biological theories of his time. 



