1 86 LILLIE AND KNOWLTON. [VOL. I. 



frog at 2 to 3 C. At this temperature some of the eggs of 

 the frog developed further, but always abnormally. The 

 abnormalities produced were of the same nature as those 

 described by Morgan and Tsuda('94), by Hertwig ('94a) and by 

 Gurwitsch ('96) in their studies on the effect of solutions of 

 halogen salts of sodium and lithium ; that is to say, abnormal- 

 ities in the region of the blastopore, principally spinae bifidae. 

 No anencephalic monsters were found. 



Supramaximal temperatures have much the same effect, but 

 the abnormalities are much more pronounced, owing partly to 

 the fact that the embryo could be reared to a much later stage. 

 In both cases the effect is undoubtedly due to the greater sensi- 

 tiveness both to subminimal and supramaximal temperatures of 

 the cells of the zuhite hemisphere, as both Hertwig and Gur- 

 witsch have remarked. The greater sensitiveness of the white 

 cells is due to the relatively greater amount of yolk in them. 



3. 77/1? Growth in LengtJi of Tadpoles of the Frog (Rana vire- 

 scens} and Toad (Bufo lentiginosus} at Different Tempera- 

 tures. 



a. Normal Temperature Range.- -The tadpoles of the frog 

 and toad were taken as soon as hatched (at the temperature 

 of the room, 18-20 C.), and two measurements were made of 

 each with the ocular micrometer under a very low power of the 

 compound microscope (13.5 divisions = I mm.); the first meas- 

 urement was the length of the tail from the anus, the second 

 the total length. By subtracting the first measurement from 

 the second we could get the length of the head and trunk, 

 but this has not been included in the tables. At the end of 

 24 hours the measurements were repeated. The tables give 

 the difference between the first and second measurements, 

 that is, the growth in length in 24 hours. The growth in 

 length of the trunk is very variable, owing to the fact that 

 it is increasing at the same time in breadth as well as in 

 depth, and more so than in length. The growth of the tail, 

 on the other hand, is almost purely growth in length, so it 

 alone is represented in the form of a curve. The tadpole is 



