476 
ME. W. H. EANSOM ON THE OVUM! OF OSSEOUS EISHES. 
tractions promptly. Also that it causes afterwards an irregular deformed projection of 
the germinal disk, soon followed by a state of complete permanent relaxation, and fusion 
of the cleavage masses into one formless mass. Ultimately it causes rupture of the inner 
sac and chemical change in the } r elk. 
The Trout. 
In this fish the impregnated ova do not exhibit any visible contractions of the yelk, 
although a breathing-chamber forms ; the formative yelk concentrates at the germinal 
pole, and its elements undergo changes like those in Gasterosteus. Cleavage did not 
take place in my experiments made in January 1855 until the next day. Prior to the 
commencement of cleavage no distinction is visible between the impregnated and non- 
impregnated eggs. I was struck with the great length of time which these unimpregnated 
eggs remained clear and unchanged in water : if the inner sac be not injured, it is at 
least twenty-three days ; while ova kept in moist airfor the same period decompose, are 
foetid, alkaline, and coagulate when put into water less than a fresh egg broken in water. 
The Ruffe. 
Impregnated eggs of the ruffe exhibit slow changes of form of the yelk-ball without 
distinct oscillations. Unimpregnated eggs in water form a breathing-chamber, and show 
similar slight changes of form of the yelk. In four minutes the formative yelk gradually 
concentrates. 
The Perch. 
Impregnated ova of perch undergo changes of form like those of the ruffe, and the 
same may be said of unfecundated ova put into water. 
The Pike. 
1. The sequences of impregnation. 
These ova are better adapted for the examination of some points than are those of 
Gasterosteus , and their study has helped me to correct some errors which I fell into at 
first. 
Impregnated eggs show a commencing breathing-chamber and slight changes in the 
droplets of the cortical layer after about a minute ; unimpregnated eggs are similarly 
affected by water only. After twenty minutes the breathing-chamber was complete, and 
the formative yelk concentrated into a well-defined discus germinativus in the fertile 
eggs, and the barren ones appeared in all respects the same. After three hours and 
twenty minutes contractions began with a slow flattening of one side of the yelk-ball 
and a slight oscillation. After three hours and forty minutes cleavage began, and up to 
this time no distinction was visible between the impregnated and the unimpregnated 
eggs. Four hours after deposition in water, in these latter the discus proligerus was not 
lobulated. 
