388 PROGRESS OF SCIENCE IN THE CENTURY. 



isation and cleavage."^ This was the beginning of 

 a long series of researches, of which the most remark- 

 able are probably those of Curt Ilerbst.f 



Herbst placed fertilised ova of various sea-urchins 

 in sea-water whose normal composition had been dis- 

 turbed by the addition of solutions of potassium 

 chloride, lithium chloride, and so on, usually in the 

 proportions of 3.8 grms. to 100 centimetres of sea- 

 water, l^othing could be quainter than some of the 

 resulting abnormal forms which nevertheless tended 

 to reach the normal (Pluteus) type by entirely 

 abnormal paths. It remains uncertain how far the 

 chemical re-agents act directly, or only by disturb- 

 ing the osmotic pressure, but Herbst favours the 

 second interpretation. 



(g) LoeVs Experiments. — Profs. O. and E. Hert- 

 wig, Prof. T. II. Morgan, and others have shown that 

 if unfertilised eggs (especially of sea-urchins) be sub- 

 jected to the influence of weak solutions of various 

 salts (sodium-chloride, magnesium-chloride, etc.) 

 or of other substances (such as strychnine), they 

 may exhibit changes comparable to those of cleavage 

 or of preparation for cleavage. 



In 1899, Professor Jacques Loeb of Chicago suc- 

 ceeded in rearing perfect larva3 of sea-urchins from 

 unfertilised eggs which had been left for a couple 

 of hours in sea-water disturbed by the addition of 

 some magnesium chloride. It seems to us im- 

 possible to find any reason for doubting the ac- 

 curacy of the carefully controlled experiments.:}: It 

 may be, however, that sea-urchin ova are sometimes 



* Jenaische Zeitschrift f. Naturwissenschaften, XX., 1887. 



■f Zeitschr. wiss., Zool., LV., 1892, pp. 446-518, 2 pis. Mt. 

 Zool. Stat. Neapel, XI. 1893, Archiv f. Entwicklungsme- 

 chanik, II., 1896, etc. 



t American Journal of Physiology, 1889 and 1900. 



