THE CELL IN RELATION TO THE MULTICELLULAR BODY 6 1 



of the echinoderm-egg the blastomeres ** spin " dehcate protoplasmic 

 filaments, by which direct protoplasmic continuity is established 

 between them subsequent to each division. These observations, if 

 correct, are of high importance ; for if protoplasmic connections may 

 be broken and re-formed at will, as it were, the adverse evidence 

 of the blood-corpuscles and wandering cells loses much of its weight. 

 Meyer ('96) adduces evidence that in Volvox the cell-bridges are 

 formed anew after division ; and Flemming has also shown that 

 when leucocytes creep about among epithehal cells they rupture the 

 protoplasmic bridges, which are then formed anew behind them.^ 



We are still almost wholly ignorant of the precise physiological 

 meaning of the cell-bridges ; but the facts indicate that they are not 

 merely channels of nutrition, as some authors have maintained, but 

 paths of subtler physiological impulse. Beside the facts determined 

 by the isolation of blastomeres, referred to above, may be placed 

 Townsend's recent remarkable experiments on plants, described at 

 page 346. If correct, these experiments give clear evidence of the 

 transference of physiological influences from cell to cell by means of 

 protoplasmic bridges, showing that the nucleus of one cell may thus 

 control the membrane-forming activity in an enucleated fragment 

 of another cell. The field of research opened up by these and 

 related researches seems one of the most promising in view; but 

 until it has been more fully explored, judgment should be reserved 

 regarding the whole question of the occurrence, origin, and physio- 

 logical meaning of the protoplasmic cell-bridges. 



LITERATURE. I •'- 



Altmann, R.--Die Elementarorganismen und ihre Beziehungen zu den Zellen, 2d 



ed. Leipzig, 1894. 

 TAnnee Biologique. — /^^7;v>, 1895-96. (Full Reviews and Literature-lists.) 

 Bohm and Davidoff . — Lehrbuch der Histologic des Menschen. Wiesbaden, 1895. 

 Boveri, Th.— (See Lists IV., V.) 

 Biitschli, 0. — Untersuchungen liber mikroskopische Schaume und das Protoplasma. 



Zt'/^z^s/;^ (Engelmann), 1892. 

 Id. — Untersuchungen liber Struktur. Leipzig, 1898. 

 Carnoy, J. B. — La Biologie Cellulaire. /./Wvr. 1884. 

 Engelmann, T. W. — Zur Anatomic und Pliysiologie der Flimmerzellen: Arch. ges. 



Phvs., XXIII. 1880. , .^ , 



Erlanger, R. v. Neuere Ansichten liber die Struktur des Protoplasmas : ZooL 



CentralbUUl-^j9' 1896. 

 Fischer, A. Fixierung, Farbung und Bau des Protoplasmas. Jemu 1899. 

 Flemming, W. Zellsubstanz, Kern und Zellteikmg. Leipzig, 1882. 

 Id. ZeW^: MerkelundBonHet^sErgebnisse,\.-\'n. 1891-97- (Admirable reviews 



and literature-lists.) 



1 '95, pp. lo-i I ; '97, p. 261 . ' See also Introductory list, p. 14. 



