-460 POLYMORPHISM AND LIFIMIISTOKY IN THE DESMIDIACE.Ii:, 



With all deference to my distinguished critic, I cannot accept 

 these statements in their entirety, as I believe they are in some 

 , i-espects erroneous. I have, indeed, quoted the remarks at 

 length, because they so clearly and succinctly set forth the 

 opposite of the facts of Desmid life, as I understand it, and I 

 , maintain that the more thoroughly the latter is investigated, the 

 more completely will the truth of this assertion be established. 

 In the first place, in Australia, in warm weather and in shallow, 

 stagnant waters, cell-division t/oes take place a second timebefoie 

 the nascent semicells have become fully developed, and it is 

 exactly this that gives rise to the multitude of degenerate forms 

 or " species." I have already given a plain proof of this in my 

 tirst paper (These Proceedings, p. 197, 1907, Plutes ii.-v.) from 

 specimens all found in one locality, many years ago. On PI v., 

 fig.24, is shown a semicell of Cos', veuustum, and of this species fig. 

 26(left figure) is a young form(Cos. trilobidattim Reinsch, forma) 

 , developing into a typical Cos, veuustum through fig. 26 (right 

 - figure), 'I'he middle figure of the three shows a mixed form of 

 Cos. trllobnlaluni, and an immature form (f. incogtiita Playf. ); 

 while in tig.25 the latter is sliown as a complete cell. ]n what 

 . way could fig.25 have come into existence except by division of 

 ., the mixed furm 1— A-t- l>, at division, becomes A + A and B+ l^>. 

 Agfii", on Pl.xi., of the present paper, tig 7 shows a chain of 

 eight semicells, which has come about in this way. A, A, formed 

 the original cell, B,B, are the semicells resulting from the first 

 division. Before these semicells aie full-grown, or even discon- 

 nected, a second division has taken place in both cells (almost- 

 idways in both, showing that it is the outcome of external 

 influences affecting all alike) and C,C, D,D, are produced This 

 specimen was abstracted from a small phial containing living 

 Desmids; before they were disturbed, tully a score of such chains 

 could be observed, with the aid of a Coddinuton lens, adhering to 

 the glass. On account of their fragile nature, such chains are 

 not often f lund in gatherings, though halves are not infrequent 

 — three immature semicells, and a more mature fourth; rj. 

 Pl.xi v., figs.9-10. In hot weather, and in shallow stagnant 



