500 
DE. W. H. EANSOM ON THE OVUM OE OSSEOUS FISHES. 
PLATE XVIII. 
Fig. 63. The inner sac contracted by repeated applications of the current. Electrolytic 
changes visible. 
Fig. 64. Final result after repeated application of the galvanic current. 
Figs. 65 & 66. Contractions, the effect of zero-galvanic currents, too weak to cause 
rupture of the inner sac. 
Figs. 67 & 68. Contractions excited by weak galvanic currents in eggs which had been 
partially frozen. 
Fig. 70. Electrolytic effect of the galvanic current upon the cleavage masses. 
Fig. 71. Irregular cleavage in an egg of which the inner sac had been ruptured by 
partial freezing. 
Fig. 72. Second stage of the action of a weak solution of carbonic acid upon an egg 
before cleavage. The yelk-ball globular ; the germinal disk very prominent 
and conical (drawn seventy minutes after impregnation, and thirty-five mi- 
nutes after the action of the carbonic acid). 
Fig. 73. First stage, four minutes after the action of carbonic acid upon an' 1 egg, after 
the first cleft is complete. The yelk-ball globular, the germinal disk 
retracted. 
Fig. 7 4. Last stage of the action of carbonic acid on an egg in the same grade of develop- 
ment, not ruptured or chemically changed. The food-yelk globular and still, 
the cleavage masses fused and diffused. (The breathing-chamber is too large.) 
Fig. 75. Final stage of the same eggs when the inner sac had ruptured and chemical 
change taken place. 
Fig. 76. Normal aspect of the germinal disk cleft in four masses (as standard of com- 
parison). 
Figs. 77 to 79 inclusive. Stages of the recession of the germinal disk into the yelk, 
which took place during the first few minutes after the action of the carbonic 
acid. 
Figs. 80, 81 & 82. Stages of the gradual reprotrusion of the germinal disk, with com- 
mencing fusion of the cleavage masses. 
Fig. 83. State of complete fusion of the cleavage masses, three hours after the action 
of the carbonic acid. (The yelk-ball should more nearly fill the yelk-sac.) 
Postscript. 
Partly from an unwillingness to enter upon any discussion as to priority, and partly 
not to add to the length of this paper, I avoided historical references entirely. But as 
my silence might seem to indicate an acquiescence in claims which are unjust to other 
observers, I have since thought it better to append a short history of the observations 
relating to the micropyle in Fishes. 
