PAR THENOGENESIS 



this case the percentage of development is not so high as 

 that obtained by use of the method just mentioned. 



Eggs of sea-urchins, fertilizable after complete matura- 

 tion, early became the favorite objects for experiments on 

 induced parthenogenesis. 



Although Morgan made experiments which indicated that 

 by means of treatment with hypertonic sea-water, eggs of 

 Arbacia can be induced to develop parthenogenetically, he 

 failed to extend his studies sufficiently and thus to obtain 

 the production of larval forms from unfertilized eggs. 

 Despite this failure his work demonstrated that treatment 

 with hypertonic sea-water can call forth the establishment 

 of the mitotic complex, the sign that development has been 

 initiated. By extending Morgan's work, J. Loeb was able 

 to induce eggs of Arbacia to develop parthenogenetically to 

 swimming forms.' He deserves the full credit because he 

 appreciated his findings, whilst it appears that of his pre- 

 decessors, Greef, O. and R. Hertwig, Mead and Morgan, 

 only Mead experimented with the definite purpose of induc- 

 ing development by chemical means. 



Loeb found that, whilst after exposure for two hours to a 

 solution of 50 cc. of sea-water plus 50 cc. i^g M MgCU, 

 the eggs of the common sea-urchin, Arbacia, found at Woods 

 Hole, Mass., developed into swimming larvae, the use of 

 other salt solutions gave no results. The next year, work- 

 ing on the California coast with eggs of the sea-urchins, 

 Strongylocentrotus purpuratus and .S, franciscanus, he was 

 able to induce development not only with MgCU, but also 

 with NaCl or KCl, either of these salts being added to 

 sea-water, in the proportions 10 cc. of a 2.5 gram molecular 

 solution to 90 cc. of sea-water. Later, other salts as well as 

 cane sugar and urea were also found to be effective. This is 

 the so-called old or original method of parthenogenesis. 



' See Loeb /p/J and earlier. 



2ig 



