EXPERIMENTS ON THE REARING OF FISH LARVA. 207 
coal filter a scum of bacteria in the zoogloea form soon appeared on 
the surface. I therefore replaced the charcoal filter by sand filters 
made in a box or bottle, during the whole experiment supplying 
water only through some kind of effective filter. 
On March 10th flounder and plaice eggs were first seen at the 
surface of the large tank, containing flat-fishes, in the aquarium, On 
the 12th I collected a considerable number and put them in a hatch- 
ing jar, and shortly afterwards placed others in a second hatching 
jar. It was not practicable to separate the larger plaice eggs from 
the smaller ones of the flounder. On the 19th the flounder eggs 
were found to be hatched; the plaice larvee began to emerge on the 
22nd, and on the 24th I turned all the larve out into one of the 
Laboratory tanks, the inflow of water passing through a filter of sand 
and gravel contained in a glass jar. I fed them as usual, partly 
with egos of Nereis, partly with strained material from the tow-nets. 
On the same day I put some of the larvee into a bell-jar filled with 
water brought in from the open sea. In the tank, in addition to 
the inflow of water I arranged a delivery of air in small bubbles at 
the bottom of the tank, thinking that this would serve two purposes, 
to aérate the water and to keep the food-particles suspended. 
The plaice larve lost the yolk and began to feed on March 27th. 
They took the worm food more readily than the hving material from 
the tow-nets. On April 2nd they were nine days old, and at this time 
the very fine primordial rays had appeared in the posterior part of 
the larval median finmembrane. On April 9th there were not many 
surviving, and in these no great advance in development was visible, 
but the commencement of the formation of the permanent caudal fin 
was indicated. ‘he number steadily diminished, and the last speci- 
men was seen on April 23rd, when it was thirty days old. In these 
older specimens the formation of the permanent fin-rays had not 
commenced, still less had the rotation of the eyes begun to take 
place. 
The larve in the bell-jar in water from the open sea lived a much 
shorter time; the last was seen on April Ist. 
Another lot of plaice larvee were hatched on April 9th, and I 
turned them out into one of the Laboratory tanks supphed with water 
directly from a jet without filtration, and I provided no air supply. 
I fed these very carefully on the usual worm food, which they took 
readily. I carefully washed the food, so as to keep out as much as 
possible the blood and soluble matters derived from the worms. 
These larvee began to die off as usual after some days, but two were 
seen alive on May 16th, when they were thirty-seven days old, or 
five weeks and two days, which is a much longer period than I have 
succeeded in keeping them before, 
