They are formed of a nucleus which stains deeply, invested by a very delicate layer of protoplasm. At the junction of somatopleure and splanchnopleure they are more rounded than elsewhere. Very few loose connective-tissue cells are present. The cells just described vary from .008 Mm. to .01 Mm. in diameter.
The primitive ova are situated amongst them and stand out with extraordinary clearness, to which justice is hardly done in my figures.
The normal full-sized ova exhibit the following structure. They consist of a mass of somewhat granular protoplasm of irregular, but more or less rounded, form. Their size varies from .016 - .036 Mm. In their interior a nucleus is present, which varies from .012 - .016 Mm., but its size as a rule bears no relation to the size of the containing cell.
This is illustrated by the subjoined list of measurements.
| Size of Primitive ova in degrees of micrometer scale with F. ocul 2. | Size of nucleus of Primitive ova in degrees of micrometer scale with F. ocul 2. |
| 10 | 8 |
| 13 | 8 |
| 13 | 8 |
| 14 | 7 |
| 15 | 7 |
| 13 | 7½ |
| 11 | 8 |
| 16 | 5½ |
| 12 | 7 |
| 10 | 7 |
| 15 | 6 |
| 13 | 6 |
| 12 | 7 |
The numbers given refer to degrees on my micrometer scale.
Since it is the ratio alone which it is necessary to call attention to, the numbers are not reduced to decimals of a millimeter. Each degree of my scale is equal, however, with the object glass employed, to .002 Mm.
This series brings out the result I have just mentioned with great clearness.
In one case we find a cell has three times the diameter of the nucleus 16 : 5½; in another case 10 : 8, the nucleus has only a slightly smaller diameter than the cell. The irrationality of the ratio is fairly shewn in some of my figures, though none of the largest cells with very small nuclei have been represented.
The nuclei are granular, and stain fairly well with hæmatoxylin. They usually contain a single deeply stained nucleolus, but in many cases, especially where large (and this independently of the size of the cell), they contain two nucleoli (Pl. 12, figs. 14c and 14d), and are at times so lobed as to give an apparent indication of commencing division.