490 
DE. W. H. EAInSOM ON THE OVUll OE OSSEOUS EISHES. 
ments with that which takes place in cell-development and multiplication, and in the 
muscular movements of the embryo, a third series of observations was made on more 
advanced developing ova of the pike, and on recently hatched embryos. In this series 
I employed the same cells, and using the same bulk of organic matter of the same kind, 
in different grades of development, I observed how the duration of the different activi- 
ties varied. 
Experiment n . — Two healthy developing ova were put into a cell in water, and sealed 
with hot tallow, seventy-six hours after impregnation, when the yelk-contractions were 
very vigorous, and no muscular movements of the trunk or contractions of the heart 
could be seen. Seven hours after, but little progress in the development was seen ; the 
yelk-contractions were vigorous. Eighteen hours after, no further development, and no 
yelk-contractions were seen : the embryonic tissues were not opaque. Forty-eight hours 
after, the tissues were somewhat opaque, and the germs of the vertebrae were partially 
fused together. 
Experiment o was similar to the above, using two eggs 101 hours after impregnation, 
when the yelk-contractions were vigorous, but no beating of the heart or movements of 
the trunk were seen. Seven and a half hours after, the contractions were visible, but 
somewhat reduced in vigour ; a barely recognizable progress in the development had 
occurred. Eighteen hours after, no further progress had been made in the development 
of the organs, and all motion had ceased. The ova were much behind the control eggs, 
and the tissues were still clear. 
Experiment was similar to the above, using two healthy eggs 127 hours after im- 
pregnation, when the yelk-contractions were distinct. The germ of the heart was visible 
but was not seen to move, the trunk struggled rarely and fitfully. After 134 hours all 
movement had ceased. 
Experiment q was similar to the above, using two eggs 150 hours after impregnation, 
when the yelk-contractions were vigorous, the heart was beating regularly, and the 
trunk frequently moving ; a few circulating corpuscles were seen. After 6^- hours the 
heart was still, the trunk was not seen to struggle, nor could I by using the micrometer 
thread detect any yelk-contractions. 
Experiment r was similar to the above, using two healthy eggs 174 hours after im- 
pregnation, when the heart was acting vigorously, the stream of blood was seen entering 
the auricular opening, the trunk often moved, and the yelk contractions were well seen. 
After 7f hours the movement had ceased in one egg, in the heart, trunk, and yelk. In the 
other the heart was moving slowly, and feeble trunk-movements were seen, but no yelk- 
contractions. In this egg the heart was irregularly and slowly acting after twelve hours. 
After eighteen hours all was still. The discrepancy which this result shows as com- 
pared with experiment q, is explained by the fact that there were several deaths in the 
dishes from which the eggs were taken, and some parasitic growth on the yelk-sacs, 
which I neglected to wash off in the case of experiment q, but carefully attended to in 
experiment r, in which instance I also selected the eggs under a lens. 
