^Q S. GOTO. 



bipolar cells, hut there are also among them multipolar cells (PI. XXIY, 

 fig. 5); and unlike wliat is seen in the other genera, the fibres proceed- 

 ing fi-om them can he very distinctly followed for a considerable 

 distance. These fibres are direct continuations of the protoplasm of 

 the cells, are destitute of any sheath, and run in the long direction of 

 the brain, i. c, at right angles to the long axis of the body. They 

 stain Cjuite deepl}' near the nucleus, but become fainter and faiiiter 

 as we follow them away from the nucleus, until they finally, in their 

 aftinity for stains, become scarcely distinguishable from the fluid which 

 fills the meshes of the connective tissue. 



In the brain are imbedded the ej/cs, when such are present. 

 Among the genera I have studied, these are present only in Tristomuiu, 

 EpihiJcUa, and j\[()nocofi/l<\ and :n*e arranged in two pairs. In all the 

 three genera jnst mentioned, their relative positions are such that an 

 isosceles trapezoid is formed by connecting them. In Tristomuiii and 

 EpihdcUa, the shorter of the two parallel sides of the trapezoid is 

 situated anteriorly, while in J\Io)iocotijIe the reverse is the case. I have 

 carefully studied these eyes only in Tristomam ovale ; and my results 

 are somewhat ditferent from those arrived at l)y Lang.'^ This 

 writer enumerates four elements ()f which a single eye is formed, ri:., 

 (1) the pigment, (2) the lens, (3) the retina, and (4) the ocular 

 muscle. According to my observation the last is no other than the 

 dorso- ventral muscles of the body which traverse the brain close to 

 the eyes, and it therefore seems to me morphologically more correct 

 to call them by that name, although physiologically they take great 

 ])art in the movements of the eyes, which are merely passive, the 

 worm having no power to direct its eyes in any special direction. 

 In the anterior eye (PI. XXIV, fig. 3) the lens is an ellipsoidal, 



1). /.(-p. -11. 



