4 J. T, CUNNINGHAM. 
Temperature to which the Ova were exposed and 
Rate of Development. 
The ova of the whiting and haddock obtained on March 30th 
were hatched at the Marine Station. The temperature of the 
water in which the eggs were kept varied from 6° C. to 9° C., 
average 7°5° C. The temperature of the sea outside the Isle 
of May at the time the eggs were taken was almost constant at 
6:1° C. The whiting hatched on the eleventh day, haddock on 
the twelfth. Some were exposed after seven days to a some- 
what higher temperature, the thermometer sometimes for a 
short time being at 13° C., and of these the whiting began to 
hatch on the tenth day, the haddock on the eleventh. Some 
of these larval whiting were kept alive eleven days after hatch- 
ing in a shallow dish, a piece of Enteromerpha being placed in 
the water with them as a source of oxygen. The cod eggs ob- 
tained March 30th all died before hatching. A few of the cod 
eggs obtained on April 3rd, at about the same temperature as 
before, hatched on April 15th, the twelfth day. It is not pos- 
sible to judge accurately from these few data how long the ova 
take to develope in the conditions obtaining in the sea outside 
the Isle of May. The haddock and cod evidently require the 
same time to reach the hatching stage, and the whiting a little 
less time than these. Probably at the temperature of 6° C. to 
7° C. obtaining in the month of March at the mouth of the 
Firth of Forth, the cod and haddock would hatch about the six- 
teenth day after fertilisation. Professor Ryder (3) gives twenty- 
one days as the time occupied in development by the cod eggs 
studied by him, but he does not mention the temperature to 
which they were exposed. 
Description of Ova. 
The fertilised ova of the cod, haddock, and whiting are in 
all respects similar to one another except in size. The sizes of 
the ova mentioned in this paper are: 
