INCLUSIONS IN EGG OF ECHINARACHNIUS 469 



visible differences in effect occurred. It should be remembered, 

 however, that minor chemical variations may easily occur with- 

 out giving rise to visible differences. 



Attention was then directed to the cytoplasmic contents of 

 the egg before fertilizaton and the changes which occur after 

 fertilization and during the early stages of development. The 

 study of the cytoplasm of the egg has certain pecuhar advantages 

 over the study of the cytoplasm of tissue cells. To be sure, 

 one does not find secretion granules or other structures associated 

 with specialized function, but there are instead those substances 

 necessary for processes of development and differentiation. By 

 the use of various methods, several types of inclusions have been 

 demonstrated and certain conclusions regarding their part in the 

 general metaboUsm of the cell have been reached. 



The work was undertaken at the suggestion of Dr. David 

 Hilt Tennent and pursued under his direction. It is a great 

 pleasure to express my appreciation of his constant and stimulat- 

 ing supervision throughout the course of the investigation. 



PREPARATION OF MATERIAL 



The material for this work was collected, fixed, and imbedded 

 at Woods Hole during July and the early part of August, 1920. 

 The particular eggs used were those of the sand-dollar, Echina- 

 rachnius parma. They were fertilized by Echinarachnius sperm or 

 Arbacia sperm, and in all cases parallel series were kept of the 

 self-fertilized and cross-fertihzed eggs. Just ('19) has shown that 

 when the eggs are normally shed into sea-water they may be 

 cross-fertihzed without special treatment. However, it is very 

 rarely that Echinarachnius females can be obtained at Woods 

 Hole which will shed their eggs. To stimulate them to shed, 

 the test is clipped around the circumference with scissors and the 

 animal placed aboral face down on a watch-glass. Although 

 this was done with individuals from practically every lot of sand- 

 dollars brought in from June 28th to August 4th, only one animal 

 was obtained during that time which shed eggs. Therefore, it 

 was necessary to open the test and shake out the ovaries in sea- 



