I2O W. W. SWINGLE. 



group. Both thymus- and beef-fed larvae ate greedily the food 

 given them. 



At the beginning of the experiment twenty larvae of both the 

 control and thymus-fed groups of larvae were measured with a 

 millimeter rule, and the average length computed. This seemed 

 a satisfactory method of procedure, considering that all of the 

 larvae came from the same batch of eggs, and consequently were 

 of the same age. 



A very convenient method of measuring the young larvae is 

 to lay them upon moistened blotting paper. The moisture in 

 the paper prevents injury to the tail and at the same time the 

 larvae are unable to lash about. 



Table I represents the measurements of twenty larvae of both 

 control and thymus-fed groups April 12, the day the experiment 

 began. 



None of -the larvae measured revealed any indications of limb 

 development when examined under the microscope. 



OBSERVATIONS OF APRIL 20. 



When examined upon this date no observable differences in 

 color or activity of the control and thymus-fed larvae were 

 noticed. None of the larvae possessed limb buds. Considerable 

 growth, however, had occurred in the larvae of both groups, but 

 in regard to length and body size, both control and thymus-fed 

 animals were about equal, as Table II indicates. 



OBSERVATIONS OF APRIL 29. 



A careful examination upon this date, of the larvae of both 

 thymus-fed and control groups failed to reveal any differences 

 in pigmentation, activity, or mortality among the animals. 

 Upon examination under the microscope, tiny limb buds of the 

 posterior extremities were observed on those larvae of the control 

 group measuring 25 mm. or over. Limb buds were observed on 

 seven of the thymus-fed larvae measuring 27 mm. and over, in 

 the thymus No. I group. 



The limb buds of the larvaa at this early stage appeared as two 

 round, blunt projections somewhat anterior and lateral to the 

 anal opening. 



