MICRODISSECTION STUDIES, III. SOME PROBLEMS 



IN THE MATURATION AND FERTILIZATION 



OF THE ECHINODERM EGG. 



ROBERT CHAMBERS. 

 CORNELL UNIV. MEDICAL COLLEGE, NEW YORK CITY. 



(From the Research Division of Eli Lilly and Company, 

 Marine Biological Laboratory, Woods Hole, Mass.) 



This paper is a record of operative work on the starfish, sea- 

 urchin and sand-dollar eggs to ascertain the morphological nature 

 of changes which take place in the egg during its maturation and 

 fertilization. Results were obtained on the effect of nuclear mate- 

 rial on cytoplasm, the nature of cortical changes in the maturing 

 and fertilized egg and the difference between cortex and medulla 

 of the egg with respect to fertilizability and to other life activities. 

 The dissection and injection of the living eggs were carried out at 

 first by means of Barber's ('14) apparatus and later with an 

 improved micromanipulator of my own design ('2i b ). A de- 

 scription of the technique as applied to microdissection has al- 

 ready been published (Chambers, 5 i8 a ). A detailed description 

 of the new micromanipulator will appear both in the Journal of 

 Bacteriology and in the Anatomical Record. 



i. THE GERMINAL VESICLE IN THE MATURING STARFISH EGG. 



Starfish eggs, on being shed naturally, have already begun 

 maturing. In order, however, to secure large quantities of eggs, 

 it has been the general custom to remove the ovaries bodily from 

 a ripe female and to cut them up in a bowl of sea water. This 

 procedure brings the eggs into the sea water in the immature con- 

 dition with germinal vesicles intact. The germinal vesicle begins 

 to disappear anywhere from thirty to fifty minutes after the eggs 

 come into contact with the sea water and maturation usually pro- 

 ceeds in a normal manner (Wilson and Mathews, '95). 



The undisturbed germinal vesicle or nucleus of a fully grown 



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