66 J. T. CUNNINGHAM. 



This increased thickness is more pronounced at the polar 

 region of the egg than elsewhere, but the two layers are thick- 

 ened to some degree over the whole surface of the ovum. The 

 structure of the prominence at the opposite pole of the ovum 

 is similar except that the growth of the threads is not so far 

 advanced, and of course micropyle, germinal vesicle, and 

 germinal disc are absent. At the germinal pole a circular 

 depression is present in the external surface of the vitelline 

 membrane, above the micropyle, as shown in fig. 12. For the 

 sake of absolute accuracy of statement I must mention that in 

 the section from which fig. 12 was drawn the same separation 

 between chorion and follicular epithelium, due to the action of 

 the hardening reagents, was present, as is shown in figs. 2 and 

 4. The length of the specimen from which the eggs I have 

 described were taken was about 15 inches. It was taken with 

 several others on haddock lines twenty-four miles south south- 

 east of the Isle of May. There were a few other specimens in 

 the same lot in which the largest ovarian eggs showed polar 

 protuberances due to the presence of the chorionic processes, 

 but the description I have given is taken from the specimen in 

 which the protuberances were most developed. 



It is necessary now to consider more minutely the structure 

 of the vitelline membrane, and to determine, if possible, its 

 mode of formation and its homologies. As seen under a low 

 power it appears, as I have said, homogeneous and structure- 

 less. In the preparations from ova hardened with chromic 

 acid and stained with borax carmine I was unable to find any 

 structure, even with the highest powers ; but in sections from 

 ova hardened with Perennyi's fluid (chromic and nitric acid 

 mixed) under a high power strise perpendicular to the surface 

 of the membrane are plainly seen. The structure thus brought 

 to view is shown in fig. 4, a, taken from a preparation of the 

 same series as fig. 4. The striee are more deeply stained than 

 the rest of the membrane ; they are for the most part parallel 

 to one another, but sometimes they branch into two. Several 

 of them are moniliform. In some cases I have traced them at 

 the external Surface of the membrane, where the latter was 



