376 NATURAL SCIENCE. dec, 



the facts, it is nuclei and not cells that seem to most of chief im- 

 portance. The idea of the continuity of the protoplasm is thoroughly 

 well-established, for plants and for animals, young and old. On the 

 other hand, the idea of units multiplying by division, which used to be 

 attached to the cell, daily receives greater justiiication as applied to 

 the nucleus. Each nucleus has a sphere of influence, most obvious in 

 the activities of division, but frequently expressed by the formation 

 of cell-walls at the limits of the sphere, or after the shrinking caused 

 by reagents, in lines which may not correspond to definite structures. 

 No doubt, when Mr. Sedgwick's more detailed conceptions are 

 published, it will be plainer whether or no he is inclined to abandon 

 this theory of units, even in its transference to the nucleus. But it 

 seems evident to us that recent work generally, and especially 

 experimental work, supports him in attaching little importance to the 

 frequent division of protoplasm into areas round nuclei, but increasing 

 importance to the presence in so-called multi-cellular organisms of 

 localised foci which multiply by division. 



Mr. G. C. Bourne on the Cell-Theory. 



Those who have been considering Mr. Sedgwick's arguments 

 will naturally turn to Mr. G. C. Bourne's "Criticism on the Cell- 

 Theory " in the Quarterly Journal of Microscopical Science (August, 1895). 

 We cannot agree, however, that Mr. Bourne's learned and ingenious 

 essay is much more than dialectic. We differ at the outset from his 

 view that Mr. Sedgwick is vague or that " the phenomena to which 

 he draws our attention have received their due meed of recognition 

 from the time that the cellular structure of tissues was first studied." 

 As we have already shown, we think that Mr. Sedgwick has 

 exaggerated the results of the devotion given by zoologists to the cell- 

 theory. On the other hand, it is quite true that in drawings of 

 embryonic and adult tissues, zoologists habitually in the last ten 

 years have represented by sharp lines the boundaries between cells, 

 and so have given to the separation of the protoplasm of cells an 

 importance that is a matter of theory rather than of observation. 

 Recognition of the existence of multinucleate Protozoa, and of 

 organisms like myxomycetes and Botrydimn, and of the continuity of 

 the protoplasm through cell-walls, is not Mr. Sedgwick's point. The 

 side of embryonic development that has been most prominent in 

 zoological writing and teaching has been the multiplication and 

 marshalling of cells : the side of histology that has been most 

 prominent is the presence of cellular units in tissues. It has been 

 recognised on all hands that the cells in embryonic and adult tissues 

 are distinct from each other in varying degrees ; but the funda- 

 mental idea has been that cells consisting of protoplasm and nucleus 

 are the unit masses. Against this Mr. Sedgwick urges the totally 

 distinct conception that while nuclei are discrete unit masses 



