GROWING LYMPHATICS AND THE MESENCHYME 353 



are fastened to the horizontals (A) by damar. The fifth side of 

 of the chamber is formed by a cover-slip (E), while the sixth 

 side is left open. Paraffin is used in order that repair may be 

 quickly made if the cover-slip is cracked or broken. A paraffin 

 coating of the floor of the chamber was found to be useful. Such 

 a cell has a thickness of about 5 mm., and a depth of from 10 to 

 12 mm. For larvae of more than 20 mm. in length, a thicker 

 cell is necessary. 



In use the slide is clamped to the stage of the microscope 

 which is arranged with the tube horizontal. The tadpole to be 

 examined is anesthetized in a small dish of chloretone solution, 

 and is transferred carefully from dish to cell by means of a pipette 

 or medicine dropper. The tadpole is brought carefully to the 

 side of the cell next the cover-glass by means of a blunt needle, 

 or by washing with a pipette. A narrow piece of cover-glass 



(D) is set on the floor of the cell, leaning against the cover-glass 



(E) which forms the front wall of the cell, and is brought against 

 the portion of the tail to be observed, by pressing gently with a 

 needle. In this way the part of the tail to be studied is held 

 firmly in contact with the cover-glass, and is protected from the 

 jarring of the water. Since the narrow piece of cover-glass comes 

 in contact with the thick central muscular portion of the tail, 

 pressure on the fin expansion is avoided. For older larvae, which 

 require more frequent changes of the chloretone solution, a special 

 apparatus was designed, by which a continuous circulation of 

 chloretone through the cell may be maintained. It is this modifi- 

 cation which is shown in fig. A. The solutionis poured into a 

 funnel, which may be raised or lowered as desired. A rubber 

 tube conducts the fluid to a fine glass canule (F) which enters 

 the chamber at the lower corner. A small block of paraffin (M) 

 protects the tadpole from the direct stream. A second glass 

 canule (G) carries off the excess of fluid from the opposite upper 

 corner. It is possible, with a cell so constructed to make obser- 

 vations with the highest powers of the microscope, even with the 

 oil immersion, for a cover-slip, only, separates the microscope 

 objective from the object studied. 



