104 PATTEN. 
distal end of the median eye nerve is unpaired, while the proximal end is paired. 
The roots of the ,-shaped nerve terminate in the semicircular lobes. 
The lateral eyes have moved backward, away from their original position 
to the dorsal surface opposite the second and third thoracic appendages, Ze. 
The “dorsal organ” has retained its original position on the fourth segment. The 
dorso-ventral muscles, dividing the yolk into segments, and passing between 
the primary liver lobes, have appeared. 
Fic. 7, X 40. Surface view of a normal embryo about four weeks old. Picro- 
nitric acid, borax carmine, clove oil. The point that will interest us here is the 
further specialization of the cephalic lobes. The median eye tubes are still 
unfused, and open by separate pores, #.¢e.¢. The proximal portion of the median 
eye nerves is seen at p.m.n., connecting the median eye tubes, m.e.2., with the 
semicircular lobes, s.2. The latter, which are formed by invagination of the 
anterior margin of the cephalic lobes, have grown inwards and backwards, so that 
they now lie on the dorsal surface of the same. They are seen through that part 
of the brain which lies over them, and which will soon give rise to the cerebral 
hemispheres. 
The olfactory organs, o./., are now visible for the first time as oval ectodermic 
thickenings on the anterior margin of the cephalic lobes, at the point where the 
future cerebral hemispheres, the optic ganglion, and the semicircular lobes meet. 
The coxal sense-organs are visible as elongated transverse ridges at the median 
margin of the base of the appendages. From these thickenings arise the enor- 
mous ganglia of the pedal nerves and the coxal sense-organs. See my paper on 
the “ Brain and Sense-Organs of Limulus.” 
