480 
DR. W. H. RANSOM ON THE OVUM OF OSSEOUS FISHES. 
The substance of the formative yelk, at least where it is collected into a discus proli- 
gerus or germinativus, appears to possess the same contractility in a less degree (it may 
be that its solidity is a hindrance to its manifestation). Certainly, as the contractile 
waves pass forward to become lost at the germinal pole, the nipple-shaped form which 
the disk assumes (Plate XVI. fig. 39) is best explained on this assumption; and if, as I 
conceive, the substance of the inner sac is thicker at the germinal pole, so as to em- 
brace the whole of the discus, the production of that shape is easy to be understood. 
But the formative yelk possesses also another different contractile property, by which, 
when acted on by water or the maternal fluids, it tends to subdivide itself into smaller 
masses. This property it seems to be the function of the male element to regulate. 
2. Conditions of the yelk contractions and of cleavage. 
Pike ova being obtainable in greater numbers than those of the stickleback, and being 
in some other respects better adapted for experiment, the inquiry into the modifying and 
essential conditions of protoplasmic movements was continued with them. 
a. Poisons. — Morphia. A solution of the acetate of morphia of 2 grs. to 60 grs. of 
water, which had a slight excess of acetic acid, was added in small proportion to the 
water of a cell containing several ova, vividly contracting, thirty-six hours after impreg- 
nation. In less than a minute they ceased to move, the yelk-ball became round, no 
rupture of the inner sac took place. On repeating this experiment, after adding carbo- 
nate of potash in slight excess to the solution of acetate of morphia, the movements 
again seemed to cease, the yelk-ball became round in less than a minute. But a source 
of fallacy always exists in these observations, viz. that normally the yelk tends to 
become round and remain at rest for a variable but brief space of time after each wave 
has passed. Half an hour later contractions were visible. 
Acetic acid . — The above result being somewhat doubtful, a few drops of a solution 
of one drop of strong acetic acid, in sixty of water, were added to a cell containing several 
actively contracting eggs. At once an arrest of the movements took place, but the yelk- 
ball, instead of becoming round, which is the position of relaxation, remained for some 
minutes marked by the sulcus, which at the moment existed ; but afterwards the move- 
ments began again, the sulci were remarkably deep and irregular, and travelled very 
slowly. A little more of the acetic acid solution being added no effect appeared at first, 
but In two hours, three eggs out of five had become opaque by coagulation of the food- 
yelk, the two ova which remained clear being motionless and globular. 
Acetate of potash . — A weak, faintly alkaline, solution of acetate of potash was then 
added to a cell containing some eggs freely contracting. Soon the yelk-ball became 
round, the formative yelk changed in structure, became firmer, more opaque, and pro- 
jected from its surface little rounded masses. After two hours the food-yelk was still 
slowly contracting. Thus a solution of a strength which chemically changes somewhat 
the formative yelk-matter, does not arrest the contractions, although it hinders 
them. 
