484 DANIEL MAZIA 



mercaptoethylgluconamide (o-ooi-o-oi m). The purpose of the mer- 

 captoethylghiconamide, to which we were introduced by Dr. David 

 Doherty of Oak Ridge, is to block the hardening of the surface layers and 

 fertilization membrane by disulphide formation. The principle depends 

 on discoveries made at the Wenner-Grens Institute. (2) The fertilization 

 membranes are removed mechanically by passing the eggs through a fine 



Fig. 2. Mitotic apparatus isolated directly from sea urchin eggs by a new 

 method, ciescribed in the text. After isolation, the preparation was exposed to 

 5 X 10^* M CaCia. which stabilizes it and sharpens the appearance of the fibres. 



silk filter. (3) The eggs are washed in Ca-free sea water. This is very 

 important, as traces of Ca interfere with the isolation. (4) As they approach 

 metaphase, the eggs are washed in a mixture of 9 parts isotonic dextrose 

 to I part sea water to lower the ionic strength of the medium. (5) At the 

 desired stage of mitosis they are suspended in the sucrose-versene-DTDG 

 medium. Gentle shaking by hand suffices to break the eggs and free the 



