Sfraefure of an Atisfralidv Lcvd LeecJi. 221' 



by Professor Whitnian\ Dr. B. L. Maier- and Miss Merrill' of the 

 eyes of the Hirudo, Hajinadipsa, Clepsine, Macrobdella and 

 others, so in Philaeuion the eye appears to be but a more 

 specialised and highly developed segmental sense organ. The 

 most characteristic and conspicuous cells are the large clear cells, 

 each with its nucleus and vacuole. These are placed round the 

 axial fibres, as shown in Fig. 6, in a single layer. Surrounding 

 these is a cup of pigment which is shallower and less dense on the 

 outer posterior portion of the eye. Passing in at one side near 

 the base of this cup is a blood-vessel (bv) which can be traced 

 round to the other side of the cup, so that the eye is well supplied 

 with blood. The tactile cells are somewhat elongated with nuclei 

 visible at their inner ends. 



By comparison with Miss Merrill's figures the tactile cells of 

 Phi]a?mon are shorter and more like the ordinary epidermic cells. 

 With little difficulty the axial fibres in the centre can be seen. 

 These, however, in a transverse section of the eye are very 

 distinct. The optic nerves supplying the eyes pass off from the 

 supracBsophageal ganglion. In some cases the nerve appears 

 to enter the eye almost at the base, while in others it distinctly 

 passes in at the sides of the cup. Before entering the eye the 

 nerve divides, one branch being distributed to the cells and fibres 

 in the cup and the other to those at the front end of the eye (Fig. 

 7). In one section, cells could be seen on the optic nerve, 

 evidently corresponding to those called by Whitman " nerve 

 ganglion cells." 



T/ie Maj'ginal Lip Organs. (Fig. 8 and 8a). 



These are the goblet-shaped organs of Leydig. They occur only 

 in the upper lip where they are in considerable numbers set all 

 along the margin. Each consists of one or more — generally 

 more — groups of cells. 



On the surface, as in the case of the other sense organs, 

 they protrude slightly and are covered by a thin cuticle. The 



1 hoc. cit. 



- Beitriige zur Kenntiiiss dei- Hirundiiieeii-Aiij;es. Zool. .lahrhucli. Bd. v., p. 552. 



s Preliminary Note on the Eye of the Leefli. Zuol. Anzei^'., xvii., 1894. 



