470 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



must be freely permeable for inorganic salts, although, as we have 

 seen, it is not permeable for colloids. 



The two embryos develop side by side within the fertilization- 

 membrane and form swimming blastulse. At the usual time the 

 membrane bursts and sets the free-swimming embryos at liberty. 

 They are smaller than normal embryos of the same age but otherwise 

 differ in no respect from embryos which arise in the usual way. 



The opposite phenomenon, that of fusion of two egg-cells may also 

 be brought about in a certain percentage of cases by treatment of the 

 eggs with alkaline sea- water. This results in the production of gigantic 

 embryos. Even at later stages of development similar fusions may be 

 made to occur. Thus Stockard has found that fusion of the cells 

 which subsequently give rise to the eyes of a fish embryo, Fundulus 

 heteroclitus, may be caused by immersing the embryos at a certain stage 

 of their development in sea-water containing an excess of Magnesium. 

 The effect of this is to cause the development of fishes provided only 

 with a single cyclopean eye. The origin of these ajid other like phe- 

 nomena is to be sought in the influence which the composition of the 

 surrounding medium exerts upon the consistency of the protein and 

 lipoid emulsions within and at the surfaces of the cells. 



REFERENCES. 

 GENERAL: 



Harvey: Science N. S., 1909, 30, p. 694. Jour, Exp. Zool., 1910, 8, p. 355. Biol. 



Bull., 1909-10, 18, p. 269 (consult for literature) ; 1914, 27, p. 237. 

 McClendon: Science N. S., 1910, 32, pp. 122 and 317. 

 Littie, F. R.: Jour. Exp. Zool., 1913, 14, p. 515. 



Loeb: Artificial Parthenogenesis and Fertilisation, Chicago, 1913. The Organ- 

 ism as a Whole, New York, 1916. 

 Godlewsk't: Physiologie der Zeugung, in Winterstein's Handbuch der Vergleichen- 



den Physiologie, Jena, 1914, Pt. 2, 3, p. 457. 

 Lillie, R. S.: Jour. Biol. Chem., 1914, 17, p. 121. 

 CYTOLYTIC AND MEMBRANE-FORMING AGENT IN BLOOD: 



Loeb, J.: University of California Pubs, in Physiol., 1907, 3, p. 57. Pfliiger's 



Arch, 1908, 124, p. 37. Arch. f. Entwicklungsmech., 1910, Pt. 2, 30, p. 44. 

 Moore:' University of California Pubs, in Physiol., 1912, 4, p. 91. 

 Robertson: Arch. f. Entwicklungsmechan., 1912-13, 35, p. 64; 1913, 37, p. 29. 



Jour. Biol. Chem., 1912 12, p. 163. 

 Clark: Ibid., 1918, 35, p. 253. 

 SYNTHESIS or NUCLEAR MATERIAL: 



Meischer: Histochemische und Physio! ogische Arbeiten, Leipzig, 1897. 

 Loeb: Proc. 7th Int. Zool. Congress in Boston, 1907, Biol. Centr., 1910, 30, p. 437. 

 Godlewski: Arch. f. Entwicklungsmech., 1908, 26, p. 278. 

 Plimmcr and Scott: Trans. Chem. Soc., London, 1908, 93, p. 1700. 

 Conklin: Jour. Exp. Zool., 1912, 12, p 1. 



Robertson and Wasteneys: Archiv. fur Entwicklungsmech., 1913, 37, p. 485. 

 Robertson: Ibid., 1913, 37, p. 497. 



Browder: Univ. of Calif. Pubs. Physiol., 1915, 5, p. 1. 

 CHEMICAL MECHANICS OF CELL-DIVISION: 



Robertson: Arch. f. Entwicklungsmech., 1909, 27, p. 29; 1911, 32, p. 308; 1912- 



13), p. 692. 

 McClendon: Am. Jour. Physiol., 1910, 27, p. 240. Arch. f. Entwicklungsmech., 1, 



1912, 34, p. 263. 

 FORMATION OF TWINS AND MONSTROSITIES: 



Stockard: Jour. Exp. Zool., 1907, 4, p. 165; 1909, 6, p. 286. Am. Jour. Anat., 



1910, 10, p. 369. 



Loeb: Arch. f. Entwicklungsmech., 1909, 27, p. 119. Biol. Bull., 1905, 29, p. 50. 

 McClendon: Am. Jour. Physiol., 1911-12. 29. p. 289. 



