One difficulty is, that the spermatic fluid mixes very readily with water; and I cannot imagine how its virtue is preserved, [14] if (as I suppose must be the case) the egg is impregnated after exclusion; but I also think it probable that the ventral fins of the female serve to conduct this fluid to the place where it is needed, and the chemical affinity between it and the egg may be sufficient for impregnation.

P.S.  July 27th.  I tried to hatch some of the eggs I had endeavoured to fecundate.  The attempt was unsuccessful.  I placed the eggs, which I had put into some clean-washed gravel, in a shallow vessel (open at the top, and with holes drilled through the sides) in a small stream of water, but I found to my great mortification on looking for them a day or two after that there was not one left, but that in their stead were many aquatic insects, which had no doubt feasted on them as long as they lasted, and after this I was not able to meet with another shoal of Minnows in the act of spawning.

The head of the Minnow in the spawning season is spotted over with small white knobs, apparently osseous in their structure, which make their appearance immediately before the fish begins to spawn, and which disappear again as shortly after, and I think they are intended as a protection to the head of the fish during the spawning; as I remarked that they generally thrust their heads in between two pebbles, and had their tails sticking up almost perpendicularly.  Yet this was not always the case, as they sometimes ran nearly out of the water, and it was in this situation that I observed what I have before mentioned, as I found it impossible to discover anything that was done by those in deeper water; for when a female went into such a situation, there was such a crowd of males rushed to the place that I lost sight of her in a moment.

I was astonished to find how quickly the eggs were hatched.  I discovered a large shoal spawning on the 11th of May; on the 12th they were diminished to one-tenth of the number, and on the 14th (the 13th being Sunday) there was not one left.  As I had by no means satisfied myself on the subject, I felt disappointed that they had so soon finished their operations, and I took up a handful of the gravel where they had been spawning, and examined it with the microscope, to see whether I could discover any ova, and how they were going on, when to my great surprise I found them already hatching and some of them already excluded from the egg.  One of them, which I took on the point of a knife, swam briskly away, and another was the means of pointing out an enemy to me which I had not previously suspected, and that I had always hitherto believed to be the prey of and not the preyer upon fish.  The poor Minnow had somehow got fast to the point of the knife, and in its struggles to free itself it attracted the attention of a creeper—­the larva of one of the aquatic flies called drakes (Ephemerae)—­which pounced upon it as fiercely as the water staphylinus does on the luckless tadpole, but, fortunately for the Minnow, either the glittering of the knife-blade or the motion of my hand, scared it away again without its prey.