INFLUENCE OF THE MEDIUM 129 



active. Sperms which were placed in the strong solution 

 lost their irritability, but regained it upon being returned 

 to sea-water. Another instance which seems to show the 

 partial loss of irritability by protoplasm from which water is 

 osmotically extracted, is stated by the same author in the 

 same article. Hearts of ascidians, crustaceans, and of 

 embryo and adult vertebrates all beat less rapidly in strong 

 solutions than in weak ones. 



Morgan 1 repeated Loeb's experiments on Arbacia eggs 

 with practically identical results. He made the added 

 observation that the free nuclear division described above 

 occurs in concentrated solutions, even though the eggs have 

 not been fertilized. This author also gives valuable cyto- 

 logical notes on the nature of the free nuclear division. 



This paper by Morgan has been followed by several 

 others by Loeb, 2 the results of which may be brought 

 together as follows : Unfertilized eggs of Arbacia, Strongy- 

 locentrotus, and Asterias, can all be made to develop parthe- 

 nogenetically, if they are first placed for a time in sea-water, 

 the concentration of which has been raised by addition of 

 either an electrolyte (such as NaCl or MgCl 2 ) or a non- 

 electrolyte (such as cane sugar or urea). They must then 

 be returned to normal sea-water. In this artificial par- 

 thenogenesis development continues until the animal is in 

 the Pluteus stage. This is as far as the development of 

 normally fertilized embryos can be carried in aquaria. The 

 author concludes that " there can be no doubt that the essen- 



1 T. H. MORGAN, " The Effect of Salt Solutions on Unfertilized Eggs of Arbacia," 

 Science, N. S., Vol. VII (1898), p. 222. 



2 J. LOEB, "On the Nature of the Process of Fertilization and the Artificial 

 Production of Normal Larvae (Plutei) from the Unfertilized Eggs of the Sea 

 Urchin," Am. Jour. Physiol., Vol. Ill (1899), pp. 135-8; IDEM, "On the Artificial 

 Production of Normal Larvae from the Eggs of the Sea Urchin (Arbacia)," ibid., 

 Vol. Ill (1900), pp. 434-71; IDEM, "On Artificial Parthenogenesis in Sea Urchins," 

 Science, N. S., Vol. XI (1900), pp. 612-14; IDEM, "Further Notes on Artificial Par- 

 thenogenesis and the Nature of the Process of Fertilization," Am. Jour. Physiol., 

 Vol. IV (1900), pp. 178-84; IDEM, "Artificial Parthenogenesis in Annelids (Chaetopte- 

 rus)," Science, N. S., Vol. XII (1900), p. 17Q. 



