18SG.] 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 Protopterus. 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 indistinr/uishable 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 

 witliin this a number of nucleoli and granules. 



These cells appeared to be in a condition of active multiplication, 

 the various stages of wliich are indicated in Plate XXIX. figs. 9-20. 

 In fig. 10 the nucleus is constricted in the middle ; in fig. 1 1 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 k\\ 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 hkely 

 explanation of their occurrence, especially since they are only to be 

 seen in comparatively young ova. The vvhite yolk-spheres of birds ' 

 are rounded bodies containing one or more highly refractive nucleus- 

 hke bodies in their interior ; but these apparent nuclei are really 

 ' Foster and Balfour's 'EleniPnts of Enibi-yology,' p. U>. 



Proc, Zool. Soc— 1880, No. XIX. 19 



