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Part III. — Sixteenth Annual Report 



that the connection of the pouches with the germinal epithelium and the 

 wall of the ovary ceases. They appear to become detached, and the 

 epithelium may be traced as a thin single layer, the cells being small and 

 rather cubical or rounded than columnar, over the now very attenuated 

 wall of the ovary. The detached follicles, pouches, and debris must either 

 be extruded later or absorbed. The condition of the epithelium points to 

 an exuviation taking place, and the gelatinous matter probably consists 

 not only of mucin secretion but of the great mass of the cells also which 

 have undergone mucoid degeneration. 



The almost mature egg of the angler, separated from its gelatinous 

 matrix, measures about l*7mm.; it is spherical, with an extremely thin 

 capsule, about O'OOGmm. in thickness, in optical section ; in mounted 

 sections it measures only 0'004mm., and consists of a single layer. It 

 has a specific gravity of 1034. On examination with a lower power it is 

 semi-translucent, several oil-globules of different sizes being apparent, and 

 numerous yolks-pherules ; by reflected light it has the whitish, watery, 

 and granular appearance of a melting snowball (fig. 5, PI. II.). The 

 germinal vesicle cannot be detected in these eggs in the fresh state. On 

 rupture under the cover-glass oil droplets and yolk-spherules of various 

 sizes pour out. A section of a piece of an ovary containing these almost 

 ripe eggs is shown in fig. 13, PI. II. They measure in section about 

 1 •4mm. ; the yolk-spherules have fused into large droplets here and 

 there, which appear in section as somewhat rounded or irregularly- 

 shaped curdled masses, mostly towards the periphery of the egg. In 

 the centre the spherules are as a rule much smaller and more like their 

 condition in the previous opaque stage. In some of these sections an 

 excentric germinal vesicle, in process of degeneration, is present. 



I shall now briefly describe the character of the ovarian eggs in other 

 sections, beginning with the smallest. I have not yet attempted specially 

 to trace the formation of the primitive ova from the germinal epithelium, 

 but some of the appearances seen may be described. The earliest stage 

 in the formation of the ovigerous pouch consists in a slight papillary or 

 broadly conical elevation of the columnar epithelium covering the floor of 

 the ovary. The space below this elevation is clearer than the subjacent 

 tissue, and minute clear spherical cells can be seen in it, apparently aris- 

 ing from the proliferation of the basal cells of the epithelial layer. In 

 larger cones one may see the loose connective-tissue stroma, which con- 

 tains numerous nuclei, occupying the interior, with capillary blood-vessels 

 and also the smaller eggs. In a section of an ovary from a fish (size 

 unknown) captured on 5th March, preserved in platino-aceto-osmic 

 mixture and stained with eosin and hsematoxylin, the young ovigerous 

 pouches are well seen. There are no traces of old follicles. The epithelial 

 lining is well marked, and composed of a single layer of low columnar clear 

 cells. The following features are visible with the 2mm. immersion lens of 

 Zeiss and compensating ocular 4 : — At the narrow part of the stalk of a 

 pouch, where the epithelium becomes reflected on to the latter, the cells 

 are somewhat irregularly heaped up, many are oval and some spherical, 

 and each contains a small brightly- stained nucleus and a very scanty 

 ill-defined network in quite clear unstained contents. On the sides of 

 the pouch the cells become oval and then flattened to form its covering; 

 but at the part where the epithelium passes from the stalk to the base or 

 side of the pouch there is an interruption of its continuity, and minute 

 cells are to be found under the epithelial layer. These seem to be 

 detached epithelial cells which have insinuated themselves into this posi- 

 tion, and they constitute the smallest ova that can be distinguished as 

 such with certainty. 



