24 
POPULAR SCIENCE REVIEW. 
our figures. Thus fig. 9 shows the bacillar stratum enveloped 
in pigment, with the curiously varied form of the single bacilli, 
cross sections of which in fig. 10 exhibit the cruciform disposi- 
tion of its substance in different parts of its course. Fig. 1 1 
shows the complete bacillum in detail : its club-shaped swelling 
below as it springs from the optic ganglion : its nerve-like thread 
in the middle, and its four-lobed mass (darkly pigmented) at its 
termination immediately beneath the cornea : also its enveloping 
sheath with nuclei on the inner wall. These three figures re- 
present the structure as seen in the eye of the cray-fish. In 
fig. 12 (Herbstia) a still more strongly marked change of form 
is seen. Below, the same club-shaped expansion ; then a dimi- 
nished rod-like portion, which soon swells into a very distinct 
four-lobed mass containing nuclei in each lobe ; then from the 
top of this a narrowed thread rises, which swells for the third 
time into a four-lobed highly refractive and delicate mass of 
transparent substance immediately under the corneal lens. The 
sheath closely invests this singularly shaped body, and is seen 
free only in the small space between its apex and the superja- 
cent corneal lens. In fig. 14 (eye of Procrustes) the nerve is 
seen springing from its optic ganglion, and swelling immediately 
into a spindle-shaped mass (cruciform in section) which is dis- 
tinctly striated : then a finer thread runs on and forms a second 
small four-lobed knot, from which again the nerve rises and swells 
a third time into a pyriform four-lobed mass which nearly 
touches with its apex the inner facet of the cornea. Its sheath 
is straight and invests the nerve loosely. Fine tracheae run up 
within this sheath ; and also (on the left hand) two muscle fibrillse 
(!) run up within the sheath, and are lost on the membrane 
investing the upper four-lobed swelling. (In all these prepara- 
tions the pigment is removed by solution of potash.) In fig. 13 
(Dynastes) the nerve shows an elongated swelling, continued at 
the middle into a fine thread which ends in a small four-lobed 
knot, from the top of which the nerve again rises and soon ex- 
pands into a terminal pear-shaped mass touching and partially 
embracing the inner curved facet of the corneule above it. In 
fig. U) (Schizodactyla) the nerve undergoes little change of 
form until it approaches the cornea, where it swells into a pyra- 
midal l>o(ly. Tlie left-hand bacillum is figured with a crust of 
pigment ; that on the right hand is figured as it appears after the 
j>iginent is removed, by which the continuity of substance of the 
whole nerve structure is better shown. In fig. 4 Plate XXXVII. 
f I.ilielbda) two bacilli nearly resembling in form those repre- 
sented in tig. l.j (.Mantis) are seen. In both the simpler form 
of ( ‘-nieal swelling below and above clearly shows the anatomical 
continuity of the whole nerve. In fig. 18 (Acridium) the nerve 
ri;re« in the middle of the sheath accompanied by muscle fibrils 
