MATURATION OF THE EGG 245 



is dissolved or liquefied in the course of several hours (at 15 C.) 

 and the eggs then become spherical. The maturation of the 

 egg begins, but is not completed, as the polar bodies are not 

 extruded. If the concentration of the hydroxylions in sea- 

 water is increased (by the addition of NaOH or NH 4 OH) the 

 polar bodies are also extruded and the eggs are able to develop 

 into larvae. But if no alkali is added to the sea-water 

 the eggs go to pieces in the course of the next twenty- 

 four hours by disintegrating into small drops or fragments. 

 From these experiments it follows that the slight concentration 

 of hydroxylions present in sea-water sets in action the matura- 

 tion processes in the egg, but not enough to complete this 

 process for the egg. 



If a trace of saponin is dissolved in sea-water and the eggs of 

 Polynoe (that have been a few hours in sea-water) are placed for 

 one minute in this weak saponin solution, they form a perfect 

 fertilization membrane and in the course of from five to thirty 

 minutes extrude the polar bodies, after having been transferred 

 to normal sea-water. The eggs must, however, be thoroughly 

 washed in sea-water to remove every trace of saponin. 1 



In the egg of Chaetopterus, another annelid, maturation starts 

 in sea-water, but cannot be completed unless a spermatozoon 

 enters the egg. As has already been noted, Mead observed 

 that the addition of some potassium to the sea-water brought 

 maturation to completion. 2 In Thalassema also the sperma- 

 tozoon enters the immature egg and causes both the extrusion 

 of the polar bodies and development. Lefevre found that the 

 treatment of the eggs of this form with acid caused both their 

 maturation and development. 3 



1 Loeb, " Ueber die Entwicklungserregung unbefruchteter Annelideneier 

 (Polynoe) mittels Saponin und Solanin," Pfliiger's Archiv, CXXII, 448, 1908. 



2 Mead, Biological Lectures delivered at Woods Hole, 1898 (Boston: Ginn 

 & Co.). 



3 Lefevre, "Artificial Parthenogenesis in Thalassema mellita," Jour. Ex per. 



Zooi., iv, 91, ioor. 



