ZooL.— Vol. III.] HEATH— EPIDELLA SQUAMULA. 131 



dorsal surface of the brain. As Lang (1881) has stated 

 for Tristomum molce, they are located "in den vier Ecken 

 eines niederen Trapezes, dessen Basis nach hinten gekehrt 

 ist. Sie liegen ferner so, dass die Offnungen der Pigment- 

 becher je der zwei auf einer Seite liegenden Augen einander 

 zugekehrt sind. Bei Beobachtung des lebenden Thieres hat 

 man ofter Gelegenheit zu sehen, wie die vier Augen simul- 

 tan eine zuckende Bewegung ausfiihren. Dies thun sie 

 meistens nach ziemlich langen Zwichenraumen und zwar in 

 der Weise, dass je die zwei Augen einer Seite gegen einan- 

 der zu zucken." In £. squamzda one pair of eyes usually 

 moves simultaneously with the other, though this is by no 

 means invariably the case. And furthermore, if the ani- 

 mals are fresh, and consequently vigorous, the movements 

 may take place with the rapidity of the pulse beat. With 

 these two exceptions, Lang's observations may be extended 

 to E . sqiiamula. 



From the study of sections and living animals, especially 

 those which have been treated with methylen blue, I am 

 also able to confirm Lang's observations regarding the 

 finer structure of the eye. As in Tristomum molce, each 

 of the four eye-spots consists of an almost spherical, 

 highly refractive, transparent body, which, in many cases, 

 contains one or two small vacuoles; but, so far as I am able 

 to judge, no nucleus is present. This lens is partially 

 covered by a cap of dark brown pigment granules. These 

 two elements are imbedded in a comparatively large gan- 

 glion cell, which has been termed by Lang " eine typische 

 Ganglion-zelle als Retina." Whether these nerve cells 

 completely enclose the lens or not cannot be said with 

 certainty. If they do, the film lying outside of the pigment 

 cup is exceedingly thin. In every case, from two to three 

 fibers arise from each ganglion cell, and extend some dis- 

 tance into the substance of the brain. Furthermore, as 

 Lang has shown for Tristomum moles, a series of delicate 

 muscle fibers is situated in close proximity to the eyes, and is 

 iustrumental in producing the rotation noted above. All of 

 these elements are constant, and the arrang/sment rarely 

 departs from the plan shown in fig. 18. 



