178 WHEELER. [Vot. IX. 
6. Nervous System. 
The great transparency of Syucelidium makes it a very 
favorable object for the study of the nervous system. The 
brain and main nerve-trunks may be readily seen in the living 
animal, but this method is insufficient for a study of details. 
It is, however, only necessary to stain with alum cochineal, 
extract as much of the stain as possible with water, dehydrate 
and mount directly from absolute alcohol in gum sandarac to 
obtain a diagrammatically clear picture of all but the very 
finest details of the nervous system.! The nerves stand out 
as white lines on a darker background. Fig. 3 is a camera- 
drawing from such a preparation, the color of the nervous 
and non-nervous tissue being reversed for the sake of greater 
clearness. 
The two longitudinal trunks (Fig. 3 vzv) gradually widen 
anteriorly and unite to form the brain (7) which, like the 
brain of Guzda (Lang, ’814) and other Triclads, may be divided 
into an anterior and superior, or sensory, and a posterior and 
inferior, or motor portion. From the former portion arise, on 
either side of the median line, three sensory (?) nerve trunks, 
which run forward and outward. The two inner trunks (az, 
an”) break up into a plexus before they reach the marginal 
nerve (#zv) which runs around the entire periphery of the 
body. The third nerve on either side remains undivided. 
The marginal nerve is very poorly developed between the tips 
of the mesial branches arising from the first sensory nerve on 
either side. Behind the brain each longitudinal nerve is con- 
nected with the marginal nerve of its own side by means of a 
very regular series of lateral nerves (/zv). I am not sure that 
the number of these lateral nerves is always constant ; in the 
specimen from which the figure was taken there were twenty- 
one, exclusive of the third and undivided sensory (?) trunk. 
Twenty of the lateral nerves on either side are connected by 
transverse nerves (¢7zv), which bridge the space between the 
longitudinal trunks. Their points of insertion in the longi- 
1 Sandarac is preferable to balsam on account of its lower refractive index. 
