602 PATTEN. [Vou. II. 
Before the segments just described are invaginated, the optic 
plate extends backward, almost the whole length of the body, 
as a thickened ridge which in every thoracic segment gives 
rise to a large sense-organ. On the median edge of the plate is 
formed a segmentally deepened furrow that gives rise to a longi- 
tudinal cord of ganglion cells. The three optic ganglia are 
segmental thickenings of this cord. The convex eye arises 
from three small sense-organs near the third thoracic segment, 
its nerve being derived from a part of the lateral cord of gan- 
glion cells. The sense-organ of the third cephalic segment 
developed into a pigmented body connected by a nerve with the 
ganglion of the convex eyes. The remaining sense-organs soon 
disappear. That of the fourth thoracic segment is very large, 
and has been erroneously described as giving rise to the convex 
eyes. 
The ventral cord and brain of Arthropods is at first composed 
entirely of minute sense-organs, which in Scorpions have the 
same structure as the segmental ones at the base of the legs. 
On the lateral edge of each ganglion of the ventral cord of 
Scorpions are two of these sense-organs, conspicuous on account 
of their size and dark color. In each segment of the brain are 
similar but still larger ones. All these sense-organs are con- 
verted into the ganglion cells of the brain and ventral cord. 
The above-mentioned facts and others will be fully discussed 
and illustrated in one of the following numbers of this Journal. 
MILWAUKEE, Feb. Ig. 
