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THE AMERICAN NATURALIST [Vol. XLIII 



large or small eggs, Chambers found from his study of sections 

 of various organs and tissues (lens, ear-vesicle, rectum, epi- 

 dermis, cartilage, muscle-fibers and blood-corpuscules) , that the 

 size of the cells of a tadpole or young frog is in direct relation 

 to the size of the examined individual. This in general agrees 

 with the results from my own work, which I hope to publish in 

 the near future, on the cells of large and small salamanders. 



Since, as was shown above, the size of the embryo depends 

 upon the size of the egg from which it develops, Chambers draws 

 the further -conclusion that the size of cells of an animal is deter- 

 mined by the initial size of the egg from which it has developed. 



In another experiment, where eggs of R. temporaria were 

 reared at two temperatures of 10° and 25° C, the tadpoles of the 

 first set (10° C.) metamorphosed two months later than those 

 of the second set (25° C), but the young frogs developed in the 

 medium with a low temperature (10°) were fully one and one 

 half times as large as those developed at a higher temperature. 

 Whether this large size was due to the low temperature or to the 

 fact that the tadpoles had been growing two months longer be- 

 fore metamorphosing, this point is not made clear. However, on 

 examining cells from the epidermis and rectum Chambers found 

 that the differences in total size of frogs, developed at a high 

 or a low temperature, extend also to their cells, so that large 

 specimens have correspondingly larger cells than small specimens. 



But the initial size of the eggs and the temperature of the 

 medium are not the only factors determining the size of the tad- 

 poles and young frogs, because large and small individuals may 

 develop even from eggs of uniform size and under similar con- 

 ditions of temperature. What has been found in regard to the 

 variations in size of the eggs may of course be also true in case 

 of the sperms, which might thus be a factor determining the size 

 of the young. At any rate, Chambers made an interesting 

 observation that tadpoles developed from eggs of the same size 

 begin to vary only after the supply of yolk has been exhausted 

 and they have commenced to take in food. It is not improbable, 

 therefore, that the variations in size result either from an insuffi- 

 cient amount of food available for some tadpoles, as is the case, 

 for instance, in growing starfishes, 3 or else the tadpoles may 

 consume unequal amounts of food under different conditions 

 of health. 



Ni 



On the Co 



pp. 17-S 



owth and Food-supply in 

 , 1900. 



