of the Fishery Board for Scotland. 



127 



the pouch, where they persist in the spent ovary ; in both cases they are 

 vacuolated cliiefly at the peripliery, and they probably degenerate. 



The cavity of the ovary is lined throughout with prominent columnar 

 epithelium (fig. 8 a, Plate 11. ), which, between the bases of theovigerous 

 pouches, may be in two or three layers (fig. 3, Plate III.). This 

 epithelium is reflected on to the surface of the pouch, wliere it becomes 

 cubical or rounded and then flattened, and it is difficult to differentiate 

 it in the earlier stages on the sides and top of the pouch. Later, as the 

 yolked eggs become large, the epithelium on the surface of the pouch 

 again assumes a cubical form. 



In the early stages gelatinous matter between the pouches is not 

 apparent. Thus in sections of the ovary of a large female caught on 20th 

 May, in which the largest eggs measured about 0'24mm. and were desti- 

 tute of yolk, the interspaces were free from it; but in a specimen caught 

 on 9th February, in which the largest eggs were full of yolk and measured 

 about 0*9 mm. (in mounted sections), the gelatinous substance formed a 

 layer ranging about O'lTmm. in thickness over the distal ends of the 

 pouches — in some places it was 0'36mm. thick. The quantity between 

 contiguous pouches was very small except in the neighbourhood of the 

 pedicles. In mounted sections of the ovary containing almost mature 

 eggs (l'45mm. in section) the layer covering the eggs measures about 

 0"32mm. in thickness, and the whole of the rest of the pouch is 

 covered by a thinner layer. The clear gelatinous matter stains 

 faintly but irregularly with hsematoxylin. With regard to the 

 origin of the gelatinous substance, Cunningham has made the very 

 natural suggestion that it arises by a modification of the outer surface 

 of the zona radiata,* but this is not the case. It is situated not only out. 

 side the follicle but outside the ovigerous pouch ; that is to say, it lies in 

 the cavity of the ovary, and it is in reality formed as a secretion by the 

 columnar epithelium. The epithelium lining the barren wall of the ovary 

 takes no part in its formation, but that between the pedicles of the oviger- 

 ous pouches, and covering the surf;i,ce of the latter, actively secrete it. The 

 whole of the cells composing the epithelium which lines the ovigerous side 

 of the ovary proliferate, swell up in an extraordinary manner, and undergo 

 a marked transformation, so that they appear as large clear vesicles, re- 

 minding one of the so-called gohlet cells of mucous membranes (fig. 13, 

 Plate II.). On surface view the cells appear polyhedral (fig. 6, Plate II.), 

 and the change that occurs might be described as a mucoid degeneration. 



When the large mature eggs escape from their follicles they pass into 

 the gelatinous secretion, and the mass is extruded no doubt gradually. 

 The process of expulsion through the narrow oviduct would appear to be 

 a matter of difficulty ; and the mode in which fertilisation takes place is 

 also a little puzzling. If insemination occurred before extrusion of the 

 eggs, impregnation would probably be facilitated ; and Yarrell, quoting 

 from Montagu's MS., states that the males and females differ, a point I 

 neglected to investigate. The males, at all events, are much more numer- 

 ous than the females, in the proportion of 100 to 26, and it is probable 

 that several males attend the female during oviposition. 



Sections of the spent ovary show the large pouches, containing the 

 winding wall of the follicles, from which the mature eggs have escaped, 

 and a considerable quantity of gelatinous substance outside, which has 

 split up into a curious comb-like structure and taken a deep stain in 

 preparations preserved in Perennyi's mixture. The small yolkless eggs 

 at the base are vacuolated and apparently degenerating, and it appears 



* " The Natural History of the Marketable Marine Fishes of the British Isles," p. 340. 

 I 



