222 P. G. HEATHCOTE. 



immersion by Reicbert) consists of a network of protoplasm, 

 cbromatin granules, and more fluid protoplasm. 



Tbe nucleolus is round, very distinct, and stains very deeply. 

 At a slightly later stage a deeply stained mass appears in tbe 

 body of the ovum ; this is possibly equivalent to the yolk-nucleus 

 described by Carus in Spiders (4). It increases and finally 

 forms a very distinct ring within the body of the ovum, as 

 shown in fig. 1, r. It is a semi-fluid mass which stains deeply 

 but does not show any structure. I have not observed any 

 appearances like those described by Balbiani in his account of 

 the yolk-nucleus of Geophilus (10). This mass of deeply 

 staining, structureless material is the first food-yolk formed in 

 the course of development of the ovum. As the latter in- 

 creases in size, the ring of deeply staining material breaks up 

 and becomes more equally distributed throughout the ovum in 

 the form of small globules, which are more deeply stained 

 than the rest of tbe cell-substance, though not so deeply as the 

 ring before mentioned. These globules increase in size and 

 gradually take the appearance of yolk-spherules, such as are 

 present in all subsequent stages up to a very late period of 

 development. Yolk-spherules continue to be formed in the 

 protoplasm of the ovum up to a considerably later stage ; such 

 spherules invariably stain deeply while quite small, though the 

 large spheres stain but slightly. I do not consider that the 

 process of formation of the first food-yolk diff'ers in any 

 essential from that of the formation of the yolk-spherules at a 

 later stage. The fully developed ovum within the ovary is 

 shown in fig. 2 ; it is of an oval form with a thick milk-white 

 shell, which is formed from the follicular envelope of the earlier 

 stages. The body of the ovum consists of a great number of 

 yolk-spherules, which are embedded in and separated from one 

 another by strands of protoplasm which constitute a network 

 extending throughout the ovum. At the periphery is situate 

 the nucleus in which is a single large, deeply staining nucleolus. 

 Examination with a high power lens (Jg- oil immersion, Reicbert) 

 shows the nucleus to consist of a network of solid protoplasm, 

 enclosing a more fluid px'otoplasm in its meshes, and of chro- 



