138 



CHAS. B. WILSON. 



out segmentation, its ends are enlarged more than those of 

 the first body, and they continue to be centres of filose activity 

 nearly to the blastula stage (cf. figs. 44, 45). 



Summary. — 1. The first polar body acquires its spinning 

 power soon after separation, manifests it chiefly in the form 

 of diffused spinning with little polarisation, and loses it early 

 in segmentation. The second body acquires this power 

 during separation or immediately afterwards, possesses a 

 marked polarisation, and retains its activity at least to the 

 blastula stage. 



2. In both bodies the poles are at either extremity of an 

 axis parallel to the surface of the egg, and the spinning 

 activities are more or less centred there. In consequence 

 these two points assume a character notably similar to that of 

 the two centrospheres at either end of the nucleus during 

 segmentation. 



3. Both bodies show in their interior chromosomes, whose 

 normal number seems to be five, but which vary greatly in 

 number as the result of partial fusion. 



4. The surface of the egg in the vicinity of the polar 

 bodies also exhibits spinning activities during and subse- 

 quent to the formation of the bodies. This spinning is quite 

 diffuse, but just after the separation of the second body it 

 becomes concentrated at two papillae symmetrically arranged, 

 one on either side of the first axis of segmentation. The 

 long spin-threads from either end of the first body connect 

 with these papillae. The internal phenomena of fertilisation 

 and segmentation are invisible through the yolk granules, 

 but may be seen in sections. 



Conclusions. — 1. The polar bodies and the egg 

 itself, in this species, are to a large extent physio- 

 logical as well as morphological equivalents. 



Evidently the half of the original egg nucleus which 

 remains within the egg retains the same characteristics as 

 the halves which are successively extruded in the polar 

 bodies, or else the latter acquire distinct characteristics 

 during extrusion — an hypothesis which is hardly tenable. 



