234 LILIAN SHELDON. 



of one of the long surfaces on the same side of the ovum, and 

 each is surrounded by a protoplasmic area. The peripherally- 

 situated nucleus had a peculiar lobed form, while the other 

 seemed to be in the act of dividing, the chromatin particles 

 representing the spindle-fibres cut through transversely. la 

 another ovum, in which two nuclei were present, both were 

 situated quite near the periphery ; but in this case the sections 

 were too thick for the structure of the nuclei to be made out. 



In the next stage, in which three nuclei are present, other 

 changes have also taken place in the ovum. These concern 

 the segmentation of the yolk. At the pole where the nuclei 

 are situated the yolk is broken up into segments, which vary 

 considerably in shape and size. The yolk-spheres at this pole 

 are smaller than those over the rest of the egg. The yolk 

 segmentation does not bear any definite relation to the proto- 

 plasmic and nuclear segmentation, but takes place quite inde- 

 pendently of it. A nucleus is present in each of three of the 

 yolk-segments, in others there is a considerable protoplasmic 

 reticulum, but no nucleus, while in others again there is no 

 trace of either protoplasm or nucleus. The nuclei are all 

 situated near together. Fig. 4 a is a section through the whole 

 egg. The section passes through one nucleus which is round 

 in form and contains a chromatin network, and is surrounded 

 by an area of protoplasm. It is situated in a yolk-segment, 

 the spheres composing which are very small. The section 

 passes through several other yolk-segments, four of which 

 contain no recognisable protoplasm or nucleus; another, which 

 is not completely segmented off from the mass of the yolk, 

 contains a small compact mass of protoplasm. The greater 

 part of the yolk is unsegmented, and is composed of very large 

 yolk-spheres. In future that part of the surface of the ovum at 

 which the nuclei are situated will be spoken of as the proto- 

 plasmic area. Figs. 4 b and 4 c are taken from other sections 

 through the same egg, and represent sections of the proto- 

 plasmic area seen under higher power. In fig. 4 b there is a 

 considerable amount of protoplasm in two of the yolk-segments 

 besides that in which the nucleus is present. The nucleus is 



