452 F. G. HEATHCOTE. 
immersion by Reichert) consists of a network of protoplasm, 
chromatin granules, and more fluid protoplasm. 
The nucleolus is round, very distinct, and stains very deeply. 
At a slightly later stage a deeply stained mass appears in the 
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. 1,7. It is a semi-fiuid 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 the 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 differs 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 (;4; oil immersion, Reichert) 
shows the nucleus to consist of a network of solid protoplasm, 
enclosing a more fluid protoplasm in its meshes, and of chro- 
