Art. XXYll. — Some Quantitative Lazvs of Incubation 

 and Gestation. 



By Alexander Sutherland, M.A. 



[Read 13th December, 1894.] 



It is known in a general way that the time required for 

 hatching out the eggs of cold-blooded animals is dependent on 

 the temperature at which they are kept. Professor Mcintosh 

 ("Nature" xxxi., p. 555) says that salmon eggs left in the sea, take 

 from 95 to 120 days to hatch, but that when transferred to a warm 

 room tliey hatch in 60 days. Bertram, in his "Harvest of the Sea,'' 

 says that herring eggs will hatch slowly or quickly according to 

 the temperature, a difference of 50 days being possible. As a 

 rule herring eggs take from 11 to 40 days, graylings from 14 t(» 

 40, codlish 5 to 42, tench 6 to 14, gurnards 7 to 35, stickle- 

 back 10 to 30, and so on, the higher the temperature the less the 

 time. But in connection with a book on which I have long been 

 busy, I required more definite information as to the relation of 

 hatching-time to temperature, and therefore I instituted a long- 

 series of hatchings of frogs' eggs. During two winters I took 

 the eggs of a species which Professor Spencer identified for me as 

 Hyla auna, and hatched its eggs in sets at graduated tempera- 

 tures. This species extrudes an unusual number of eggs, the 

 average of 14 sets that I counted being over 3000 to each. It 

 was easy therefore to get ten sets of 100 each, which could with 

 certainty be i-egarded as of similar condition. I put them over 

 lamps and kept them at temperatures, as nearly uniform as 1 

 could, ranging from 10° C. to 33° C. 



Six series of experiments thus conducted satisfied me that the 

 time required for hatching was inversely proportional to the 

 square of the excess of the tenqiorature above a certain fixed 

 tempei-ature. But in every series there occurred one or more 

 failures through accidental variations in temperature. I, therefore, 

 in September last, carried out a new series of experiments, 

 floating each set of eggs in a large body of water which could not 

 easily vary during intervals between observation. Even here out- 

 set was somewhat affected by a rise of 3° C. lasting for 4 hours, 



