130 SYDNEY J. HIOKSON. 



I. The Early Stages in the Development of 

 Distichopora. 



The ovum of Distichopora, like that of Allopora and other 

 Stylasterids, is provided with a large amount of yolk^ and lies 

 in a cup-shaped trophodisc. 



In young immature ova the germinal vesicle is situated in 

 the middle of the egg, is spherical in shape, is provided with a 

 well-defined membrana limitans, a germinal spot, and a fine net- 

 work of protoplasmic fibrils with thickened nodes (PI. 9, fig. 1). 



When examined with a high power the germinal spot may 

 be seen to contain a few clear vacuoles (fig. 2). 



In some ova with a full complement of yolk-spheres the 

 germinal vesicle is irregular in shape, and provided with 

 processes resembling the pseudopodia of amoeba. The outlines 

 of these processes are usually difficult to observe, the mem- 

 brana limitans being apparently wanting, and the intra-nuclear 

 and extra-nuclear protoplasm perfectly continuous (fig. 3). 



In these cases there may be seen a few large rod-shaped 

 granules (the chromosomes), which stain deeply with carmine 

 and other stains. 



These amceboid germinal vesicles are without doubt passing 

 from the centre of the ovum towards the periphery. In those 

 that are near the periphery the chromosomes are more 

 numerous and very much smaller than they are in those nearer 

 the centre of the ovum. In one case I have observed these 

 bodies arranged in a row parallel to the surface of the ovum, 

 and dividing the nucleus into two unequal halves (fig. 5). 



When and in what manner the polar bodies are formed I 

 cannot say, but it is probable that in some cases the nuclei of 

 the polar bodies are formed before the germinal vesicle reaches 

 the periphery, and are absorbed in the substance of the ovum. 

 The germinal vesicle finally reaches the periphery of the ovum, 

 and when it is in that position the fertilisation most probably 

 occurs. 



It is clear that the germinal vesicle must remain at the 



