140 INTRODUCTION TO CYTOLOGY 



esses originally common to all parts of the cell? If so, to what internal 

 or external factors is the establishment of this difference due in cells having 

 no initial polarity? Analogies with electrical polarity have been resorted 

 to in this connection, concerning which Harper (1919) says: "To pro- 

 vide an adequate basis for understanding the observed facts of polarity, 

 however, it seems to me that the conception of compound aggregate 

 polyphase systems is more suggestive than these attempted analogies . . . 

 In the spatial arrangement and interactions of these systems polar dif- 

 ferences of the most diversified types are bound to arise in the mass as a 

 whole and express themselves in the form and relative rigidity and surface 

 tension of different parts, as well as in the interrelations between the cells 

 of a group in contact." 



The polarity of the multicellular organism as a whole is closely bound 

 up with the polarities of its constituent cells. Harper has clearly shown 

 (1918) that in Pediastrum the position of the swarm-spores in the colony 

 which they unite to form is directly dependent upon their polarity. 

 This does not mean, however, that the polarity of the multicellular organ- 

 ism is nothing more than the sum of the polarities of its constituent 

 cells, unless we return to Schwann's simple conception of the organism as 

 merely an aggregate of independent cells. (See p. 12.) The higher 

 individuality, the colony, has its own polarity, which may be related to, 

 but is not the same as, that of its individual cells. In the ordinary multi- 

 cellular organism the polarity is an outgrowth of the polarity of the 

 fertilized egg cell rather than of the polarities of the many adult tissue 

 cells. 



In polarity, then, we encounter another problem which must be 

 brought nearer a solution before we can have any adequate understanding 

 of the relation of the cell to the multicellular organism as a whole, and of 

 the perplexing matter of organic individuality. 



Bibliography 7 



Metaplasm Senescence Polarity 

 VAN BENEDEN, E. 1883. Recherches sur la maturation de 1'oeuf, la fecondation et 



la division cellulaire. Arch, de Biol. 4. 

 BOVERI, TH. 1901a. Ueber die Polaritat des Seeigeleies. Verh. Phys.-Med. Ges. 



Wiirzburg 34. 

 19015. Die Polaritat von Ovocyte, Ei und Larve des Strongylocentrotus lividus. 



Zool. Jahrb. (Anat. Abt.) 14: 630-653. pis. 48-50. 

 CARRUTHERS, D. 1911. Contributions to the cytology of Helvetia crispa Fries. 



Ann. Bot. 26: 243-252. pis. 18, 19. 

 CHILD, C. M. 1911. Studies on the dynamics of morphogenesis and inheritance in 



experimental reproduction : I. The axial gradient in Planaria dorotocephala as a 



limiting factor in regulation. Jour. Exp. Zool. 10: 265-320. figs. 7. 

 1912. Studies, etc. IV. Certain dynamic factors in the regulatory morphogenesis 



of Planaria dorotocephala in relation to the axial gradient. Ibid. 13 : 103-152. 



figs. 46. 



