1886. | OVUM OF LEPIDOSIREN. 281 
The structure of these ova and the surrounding follicle is extremely 
remarkable, and quite unlike any other ova that I have seen in trans- 
verse sections of the ovary of Protopéerus. But the peculiarities of 
these ova do not end here. 
Scattered throughout the substance of the yolk are an immense 
number of cells more or less spherical in form (Plate XXVIII. 
fig. 3, c). 
These cells were limited in most cases by a very distinct external 
membrane ; their contents are a mass of rounded bodies which are 
quite indistinguishable from the yolk-spherules of the ovum, and 
strands of granular protoplasmic substance ; furthermore there is a 
distinct and large nucleus deeply stained by borax carmine, and 
within this a number of nucleoli and granules. 
These cells appeared to be in a condition of active multiplication, 
the various stages of which are indicated in Plate XXIX. figs. 9-20. 
In fig. 10 the nucleus is constricted in the middle; in fig. 11 the 
nucleus has divided; in fig. 12 the two cells have become distinct 
but lie close together ; in fig. 18 cell-division has evidently gone on 
very rapidly, as there is a nest of four cells pressed closely together 
and occupying a common cavity in the yolk. In some cells the 
amount of yolk-granules present was considerably less than in others. 
Occasionally (figs. 19, 20) the yolk-particles had run together to 
form a single large droplet. 
In a few cases I observed (fig. 15) the nucleus to be thrust 
altogether without the cells ; and here and there within the substance 
of the ovum were apparently nuclei without any cells. I am not 
inclined, however, to lay too much stress upon the last mentioned 
fact, because it would be rather difficult in any case to detect the 
boundaries of one of these cells if it were packed quite full of yolk- 
spherules. 
In other cases (fig. 13) the nucleus had become paler in colour 
(less acted upon by the staining reagent) as well as more homogeneous. 
Nuclei of this kind might easily be mistaken for larger yolk- 
spherules ; indeed my only reasons for believing them to be altered 
nuclei are their similiarity in size and shape to the more normal 
nuclei, their occurrence in cells that have become emptied of their 
contents, and the fact that they are rather more deeply stained than 
the surrounding yolk. 
Concerning the nature of these bodies there appears to me to be 
three possibilities :—either (1) they are similar to the white yolk- 
spherules of the Fowl’s egg; or (2) they are follicular cells which 
have migrated into the interior of the ovum; or (3) they are cells 
which have been formed anew within the substance of the ovum. 
The first alternative, that the structures in question correspond to 
the white yolk-spheres of birds, seems at first sight to be a likely 
explanation of their occurrence, especially since they are only to be 
seen in comparatively young ova. The white yolk-spheres of birds ' 
are rounded bodies containing one or more highly refractive nucleus- 
like bodies in their interior; but these apparent nuclei are really 
* Foster and Balfour’s ‘Elements of Embryology,’ p. 16. 
Proc. Zoot. Soc.—1886, No. XIX. 19 
