no LAWSON G. LOWREY 



A possible source of error lies in the fact that some of the litters 

 were preserved in formalin, while others were studied fresh. It 

 is well known that specimens preserved in formalin show an in- 

 crease in total weight, amounting sometimes to 10 per cent or 

 15 per cent of the total. It is, however, improbable that this 

 increase will materially affect the relative size of the organs. 



OBSERVATIONS 



The observations have been condensed into a single table, 

 from which curves expressing the relative growth have been made. 

 A brief discussion of, and explanation for, the table and curves, 

 follows. 



Table 1 gives a summary of all the observations on the differ- 

 ent litters used. In the first column will be found the serial 

 number of the litter used. In the second column, the manner of 

 preservation. . 'Form' indicates a 5 per cent aqueous solution 

 of formalin. The length of time preserved is also indicated. 

 In the third column is given the number of each sex of the indi- 

 viduals used (M-male; F-female). 



In the fourth column is given the average crown-rump length, 

 in millimeters, for the litter, the minimum and maximum lengths 

 being given in parenthesis. Similarly in the fifth column is given 

 the average gross body weight for the litter in grams, together 

 with the minimum and maximum. The net body weight is also 

 given for the later stages, in which the intestinal contents could 

 be measured and subtracted. 



The sixth column shows the average percentage by weight 

 which the head forms of the entire (net) body weight in each of 

 the various litters. The minimum and maximum percentage 

 found in the litter is given in parenthesis. Similarly in the suc- 

 ceeding columns is given the average percentage of the entire 

 (net) body weight (also minimum and maximum percentage) in 

 each litter for the brain, eyeballs, spinal cord, thyroid gland, 

 thymus, lungs, heart, liver, stomach and intestines with contents, 

 stomach and intestines empty, spleen, pancreas, suprarenal 

 glands, gonads, kidneys and (for the earlier stages) the Wolfl^ian 



