l8o BRACE. [Vol. XVII. 



secure good specimens for sectioning they were mounted on a 

 slide and held in place by a cover-glass that pressed on them 

 slightly. They were then placed on ice for a few moments 

 until chilled and unable to contract any portion of the body, 

 when they were treated with the fixing fluid. The cold also 

 prevented abnormal activity of the glands, so that very perfect 

 preparations were obtained, although the worms will go to 

 pieces if left on the ice too long. 



The fixing fluid after the second formula of vom Rath (picric 

 + acetic + osmic + platinum-chloride) was found most effect- 

 ive in demonstrating the nervous system. Specimens were 

 left in this for fifteen minutes, washed in alcohol, and placed 

 in a 20 per cent solution of tannin in acetic acid for periods 

 of time varying from twenty-four hours to four days, or else 

 they were stained in section with safranin or iron-haematoxylin 

 after vom Rath. 



Paraffin was used for imbedding, and sections were cut from 

 3-20 /A thick. Sections from 10-15 /i thick were found most 

 favorable for study. 



Nervous System. — The brain lies in front of the mouth in 

 close contact with, and partly imbedded in, the epidermal wall 

 (PI. XXI, Figs. I, 6-8), the lower part projecting more or less 

 into the cavity of the prostomium. Its ventral and lateral sur- 

 face, so far as free from the epidermis, is covered by a delicate 

 nucleated membrane which may be seen in section. It has a 

 slightly bilobed appearance, as seen from above, each half 

 having a rounded anterior margin and a large posterior lobe, 

 the latter composed entirely of nerve cells (PI. XXI, Figs. 2, 3). 

 Closely packed nerve cells with large granular nuclei cover the 

 whole dorsal surface, and are from three to four cells deep in 

 the anterior and posterior lobes, but only one layer deep in 

 the middle region where the anterior lobes meet (PI. XXI, 

 Figs. 8, 10). 



A pair of nerves composed of fibers partly from the brain 

 and partly from the oesophageal commissure, runs forward 

 from the brain into the prostomium, and another pair runs 

 back from the angle between the posterior lobes and the com- 

 missures (PI. XXI, Figs. I, 2, 5, 6, 9). 



