384 



The Growth of the Oocyte in Antedon : a Morphological Study in 



the Cell- Metabolism. 



By Gilbert C. Chubb, D.Sc, Assistant to the Jodrell Professor of Zoology, 



University College, London. 



(Communicated by Professor E. H. Starling, F.R.S. Received December 20, 

 1905,— Read January 18, 1906.) 



(Abstract.) 



In this paper I have endeavoured to interpret in terms of the cell-ineta- 

 bolism the structural changes exhibited by the growing ovarian egg of 

 Antedon bifida, Penant. The following conclusions are based entirely on the 

 study of this single type. It will be my endeavour in subsequent papers to 

 ascertain how far these conclusions are applicable to the eggs of other types 

 and to the cell in general. 



The Yolk Nucleus. — Throughout the growth of the oocyte the nucleolus 

 intermittently discharges groups of deeply basophile spherules into the 

 cytoplasm. In the young oocyte these " nucleolar spherules " remain 

 unchanged, slowly accumulating in the cytoplasm, where they form small 

 groups near the germinal vesicle. In slightly older oocytes the increased 

 fluidity of the cytoplasm which results from the progressive accumulation of 

 metaplastic material in preparation for yolk formation, causes the discharged 

 nucleolar substance to lose its spherular form, and to diffuse on to the 

 neighbouring cytoplasm. The more deeply staining area of the cytoplasm to 

 which this diffusion gives rise is the yolk nucleus. As the cytoplasm 

 becomes still more fluid, the yolk nucleus assumes the regular form of a 

 concavo-convex lens embracing the spherical germinal vesicle. 



During yolk formation the yolk nucleus passes to the periphery of the 

 egg, a migration also shared by the " peripheral spherules." The actual 

 increase in size which the peripherally placed yolk nucleus shows during the 

 earlier stages of yolk formation is speedily masked by the great superficial 

 extension and thinning out on the surface of the egg which this structure 

 undergoes during yolk formation, and which is the necessary result of the 

 great increase in bulk and surface area accompanying this process. 



As yolk formation progresses the yolk nucleus gradually loses its staining 

 capacity, and, before this process is completed, has entirely disappeared from 

 view. At no time, however, does the yolk nucleus show any indication of 

 a granular disintegration, nor does it show any spatial relation to yolk 



