338 CKESSWEI.L SHEAKKU. 



its longest diameter. Tlie spindle seems to grow witii the 

 agg. 'i'lie size of the amphiaster is always proportional to 

 that of the ovum. In the large female, where the eggs are 

 almost double the size of those of the small ones, the spindle 

 is correspondingly larger. 'J'lie size of the spindle is appa- 

 rently determined by that of the cell. 



In Limulus, according to Munson (23), the growing centre 

 of the egg is the vitaliue bod3^ This, in the early stages, 

 presents all the appearances and features of the centrosotne 

 and sphere, atid, in fact, is the centrosome of the dividing 

 ocigonia. In later stages it remains as the deKnite centrosome 

 in the cytoplasm. Thus it appears as the primitive basis or 

 centre of growtii of the cytoplasm, building this in part from 

 the granules supplied by the follicle-cells. In Histrio- 

 b del la growth does not seem confined to the region near the 

 iimphiasters, but seems to take place generally throughout 

 the cytoplasm of the egg. No yolk-nucleus or vitaline body 

 is present. In sections of fixed eggs the cytoplasmic material 

 in the immediate vicinity of the spindle is markedly less dense 

 than ill the peripheral region of the ovum. In some sections 

 the middle of the ovum appears as a space, in the middle of 

 which is the spindle with its chromosomes. 



The ovum goes through a portion of maturation during the 

 time it is still adding material to its cytoplasm. AVhile the 

 achromatic threads of the amphiaster can be readily seen in 

 the living egg, the chromosomes cannot be detected "without 

 staining. At the end of the prophase eight chromosomes are 

 found in the equatorial plate of the spindle. 



The astral rays are much less definite than the strands of 

 the central spindle. AVhile the former seem in the living egg 

 as if due to the arrangement of the yolk-granules in definite 

 lines, the latter appear as actual tlu'eads running between 

 the gi-annles themselves. In speaking of the astral rays 

 Wilson (32) says : " A careful study of their relation to the 

 meshwork in the Echinoderm, and in manv other forms 

 (especially in Nereis, Thalassema, Lamellidoris, and 

 Asterias), leaves no doubt in my opinion that tiiey are actual 



