246 



HENRY LAURENS 



The first of the methods of experimentation and the one which 

 seemed at first thought to be the most promising, but which 

 failed for reasons which will be given later, was to remove that 

 portion of the undifferentiated nervous system from which the 

 epiphysis arises. This was accordingh^ carried out on larvae 

 measuring between 5.5 and 6.1 mm. The operation is a smiple 

 one requiring but slight practice. The embryo to be operated 

 on was placed in 0.02 per cent NaCl in a watch glass, the bottom 



Fig. 5 A sagittal section of a portion of the head of a 34.0 mm. larva to show 

 the position and relative development of the epiphysis and paraphysis. 



of which was covered with paraffin. In this a little pocket was 

 dug near the middle of the dish and into this the embryo was 

 slipped so that the anterior end was directly upwards. Under 

 the binocular microscope, with a small pair of iridectomy 

 scissors, the epidermis and then the desired portion of the un- 

 differentiated nervous system was removed. The extent of the 

 portion removed is indicated approximately in figure 1 between 

 the dotted lines x — x. This operation was performed on 10 

 embryos between 5.5 and 6.1 mm. long. On 10 others in addi- 



