1896.] MICROSCOPICAL JOURNAL. 67 



rived from a single primitive individual — the ovum — by suc- 

 cessive cell divisions ; that the meaning of this mode of origin 

 is given by the evolution tlieory and that the development of 

 the higher animals is a recapitulation of the development of tbe 

 race. Mr. Sedgwick's work, however, has led him to doubt tbe 

 validity of this view of the Metazoon bod}', and he is inclined 

 to attribute a number of errors in descriptions of embryonic 

 processes to the dominating influence of the cell theory in its 

 modern form. A theory which leads to obvious errors must, 

 he thinks, be wrong, but he has not yet arrived at conclusions 

 which enable him to formulate any satisfactory alternative 

 hypothesis with regard to the meaning of the predominance of 

 the structure called cellular. 



In reference to this matter it is pointed out in Nataral Science 

 that, in the older botanical text books, the plant unit is the 

 "cell" — a cellulose chamber inclosing protoplasm and cell sap — 

 an aggregation of such cells forming a tissue. According to 

 modern ideas, however, the unit is a mass of protoplasm in 

 which is embedded a nucleus. This unit or ''energid" is the 

 starting point of every plant. It may grow and divide repeat- 

 edly without the separation of the resulting daughter units by 

 partition walls, a large number of nuclei being embedded in a 

 general mass of protoplasm contained within a common mem- 

 brane, as in Vaucheria and Mucor. In Cladophora, again, incom- 

 plete septation is illustrated, and where the completely septate 

 form prevails, the protoplasmic units, though separated, are pro- 

 bably not isolated by the cell walls. The cell has come to be 

 regarded, then, as a mere inclosure of the protoplasm, necessi- 

 tated by increase in size, differentiation and need for support. 

 Modern attention is being more and more concentrated upon 

 the necleus. Thus, whereas Weismann orginally spoke of "germ 

 cells," he now speaks of "germ plasma," meaning by that nuc- 

 lear matter ; and the continuation of the germ plasm means for 

 him the continuity of nuclear matter, rather than the existence 

 of a chain of cell division, of which the successive generations 

 are pendants. Indeed, recent work generally seems to support 

 Mr. Sedgwick "in attaching little importance to the frequent 

 division of protoplasm into areas round nuclei, but increasing 

 importance to the presence in so-called multi-cellularorganisms 

 of localized foci which multiply by division." — Am. Druggist. 



