1912] 



Blackmail — Supernumerary Median Ocellus 



95 



a single strand from the central brain mass in the median line and 

 passes directly to the ocellus without branching. The writer was 

 interested to know whether in this abnormal case the nerve sup- 

 ply would take the form of two entirely separate nerves or would 

 arise as a single nerve and later branch. A graphic reconstruc- 

 tion made by the well known method is shown in Fig. 2. The 

 nerve arises as a single one just as in the normal head and is 

 divided only in the last third of its course. As would be expected 

 from the distance between the ocellar lenses as seen in Fig. 1, there 

 is a complete division of the nerve termination, the two retinal 

 cups being entirely separate. 



Fig. 2. Graphic reconstruction of the mecHan ocellar nerve, showing its origin 

 as a single strand and its later bifurcation. X 50. 



Fig. 3. Sketch of a portion of a median sagittal section of the head, showing 

 the origin of the nerve from the brain, and the ocellar cup and lens. The fixation 

 is such as to be of value only in showing the general relations. X 50. 



The entire length of the undivided portion of the nerve is not 

 shown in Fig. 2 on account of a looping (apparent in Fig. 3) just 

 after its exit from the brain. This would of course result in a 

 considerable fore-shortening in a graphic reconstruction. Fig. 3 

 represents a sketch of a portion of a median sagittal section of the 

 head showing the proximal half of the ocellar nerve and also a sec- 

 tion of the ocelli. The histological fixation, due to the fact that 

 the material was preserved with a large number of other speci- 

 mens for ordinary dissecting purposes and perhaps was later wholly 

 or partially dried, is not such as to show finer details either in brain, 



