126 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



With the exception of the flame-cells, it has been found 

 impossible to discover any cellular elements in the excretory 

 system. The walls of the finer branches, and particularly 

 the reservoirs and lateral vessels, are excessively thin and 

 apparently structureless and devoid of nuclei. 



VIII. The Nervous System. 



The brain of E. squamiila consists of a relatively short 

 semicircular band situated near the dorsal surface immedi- 

 ately in front of the pharynx. Out of its lateral borders 

 six symmetrical nerves arise (figs, i, 2, 5), four ventral 

 and two dorsal, which extend the length of the body and 

 terminate in the posterior sucker. Both the brain and 

 these longitudinal cords give rise to smaller nerves, whose 

 general arrangement may be determined from sections and 

 stained preparations ; but with the use of methylen blue many 

 additional details appear which are otherwise hidden. A 

 small quantity of the stain is added to the sea-water in 

 which the living animals are kept, and after from one to 

 three hours various elements of the nervous system become 

 stained, and may be studied for several hours if kept cold. 

 They may also be preserved by using saturated ammonium 

 molybdate as a mordant, and then passing them rapidly 

 through various grades of alcohol and mounting in balsam. 



The large nerves which pass out anteriorly from the 

 brain are six in number (fig. 5). In addition to these, 

 from two to six extremely small fibers sometimes appear on 

 each side, but they are probably included in some of the 

 large nerves ordinarily. A short distance beyond the brain 

 all these nerves unite with a second cord, also semicir- 

 cular in form, and concentric to the brain. From this 

 commissure a number of nerves arise which supply the an- 

 terior end of the body. 



The most anterior pair of nerves arising from the brain 

 passes forward, giving off fibers to this semicircular com- 

 missure, and, continuing onward into the space between the 

 two adhesive organs, breaks up into a fine brush which ex- 

 tends into the tentacle-like projections on the anterior margin 



