OCCURRING IN THE NEIGHBOURHOOD OF PLYMOUTH. 29 



density 1 "0207 or a little more. The temperature of the water on 

 the last day in the Chester apparatus was 12*4°^ while its density 

 was not greater than 1'0260. Thus the ova were not injured during 

 the first four days by a temperature more than 4° higher than that 

 of the open sea, and a density increased on one occasion by "0033, 

 but they died on the fifth day in a circulation in which the tempera- 

 ture was the same as before, and the density decreased by "0007 or 

 somewhat more. Unless the motion or impurities from the apparatus 

 killed them, it must be concluded that they died because they sank 

 in the water. 



My next experiment was still more unsuccessful. Ova were brought 

 in on June 1st, and I transferred them to water fetched from near 

 the breakwater; the density of this was 1*0255. I added salt to 

 it till the density was 1*0265. On June 2nd the temperature was 

 14° C. I then changed the water, and placed half the ova in a 

 glass jar provided with a circulation, the outflow being protected 

 by muslin ; but on June 3rd both halves, that in the still water and 

 that in the circulating, were dead. 



On June 12th I received a number of healthy fertilized ova from 

 the " Prima Donua,^^ taken seven miles south-west of the Eddystone. 

 I placed these in a Chester apparatus, made with a perfectly clean 

 wooden tub instead of the tray formerly used, and placed them in 

 the tank-room, as the aquarium apparatus was all but complete 

 and the pumps were working. By placing the tub under one of 

 the jets I expected to obtain a constant supply of water to the 

 apparatus, which was impossible in my single room, where each 

 bucket of water had to be carried up by hand. But the pumps had 

 to be stopped and all the ova died. 



On June 29th I received a fresh supply, and as the aquarium 

 pumps were now working continuously I kept these in a Chester 

 apparatus on the shelf below the small tanks in the main laboratory, 

 water being supplied to the tub by means of a siphon from the tank 

 above. Some of these ova lived well for some days, but they sank 

 in the water because its density was not great enough. And as 

 some of the ova died the living and dead were all mixed together 

 in a mass lying on the muslin at the bottom of the jar, a condition 

 w'hich was obviously unhealthy. The water in circulation in the 

 aquarium system of the Laboratory varied somewhat in density, 

 because frequently some water had to be run off from one of the 

 large reservoirs to allow some slight defect in the arrangements to 

 be attended to, and then more water was pumped up from the shore 

 to make up the loss. On June 8th the density of the circulating 

 water was 1*0260, on August 15th it was 1*0250; it varied between 

 these two limits. On July 4th the temperature of the water in the 



