HE LEECHES OF JAPAN. 401 
lead to conclusions fundamentally different, in some important 
particulars, from those reached by Leydig and Ranke. It is 
not my intention to deal with details of history and criticism 
here, and I shall only call attention to points of special interest 
and importance in forming a correct notion of the eye. In 
passing, it may be worth while to call attention to some of the 
figures given by the above-named authors, in order to show 
wherein they are, in my opinion, misleading. In the first 
place, Leydig, whose figures are by far the most instructive of 
any that have yet been published on this subject, describes the 
sense-organs of the lip and head as goblet-shaped (‘ becher- 
formige Organe”) organs with a shallow rounded cavity 
Opening at the peripheral end. This cavity, which is only a 
depression resulting from retraction of the organ (see Fig. 4), 
is about the only justification for comparing these organs to a 
goblet. In a state of functional activity, all the sense-organs 
of the Leech are protruded, so that the peripheral end forms a 
convex surface (Figs. 2, 3 and 5) as was stated long ago by 
E. H. Weber. This cup-shaped depression of the retracted 
organ was supposed to be open at the bottom, the epidermic 
wall of the cup having a central circular perforation, in which 
the optic nerve terminated ‘‘unbedeckt.”” The optic nerve, 
penetrating the eye at the base, is represented as an ‘‘ Achsen- 
strang” running the entire length of the eye. Placing the eye 
so that he could look directly into the cup-shaped depression, 
Leydig saw, through the supposed opening at the bottom of 
the depression, a peculiar spot somewhat broader in extent 
than the “ axis-string ” seen in transverse section. In prepara- 
tions treated with reagents, this spot presented a granular 
aspect, while in a fresh condition it appeared to be composed 
of *‘ glanzenden Kiigelchen,” which represented the termina- 
tions of nerve-fibres. Ranke gives a diagrammatic section of 
the eye, in which he leaves the epidermal cover entirely away, 
and says nothing about acentral perforation. Now the peculiar 
spot seen by Leydig is probably the apical area seen in Fig, 5, 
in which the central cells of the epidermic cap present re- 
fractive rod-shaped ends. This interpretation is the only one 
