STUDIES ON THE EVES. OF ARTHROPODS: 
WILLIAM PATTEN, Pu.D. 
II. Eyes of Acilius. 
A COMPARATIVE study of the eyes offers, in my opinion, a 
promising field for the determination of the relationship be- 
tween the different groups of Arthropods. To determine 
these relationships it is necessary to understand, (1) variations 
in the structure of the eyes, (2) their topography, and (3) the 
position and structure of the optic ganglia. 
It is necessary first of all to obtain a thorough knowledge of 
some typical form. Comparison is then easy, for the problems 
solved in one case are already solved in others, while those 
left unsolved will torment the investigator in every succeeding 
study. 
In following the development of the eyes of Acz/ius I was 
forced to consider their relation, and that of the optic ganglia, 
to the brain. This required a careful examination of the de- 
velopment of the whole head. But finding it impossible to 
treat of the head without considering the rest of the body, I 
decided to confine my attention to the eyes and optic ganglia. 
Some of the figures, however, will also serve to illustrate 
certain points in the “Development of Acilius,” which will be 
the title of the paper I hope to publish in one of the next num- 
bers of this Journal. I shall reserve till then a discussion of 
the relations which the eyes and optic ganglia bear to the head 
of Arthropods. 
I. ToPOGRAPHICAL RELATIONS OF OpTic PLATE AND OPTIC 
GANGLION TO CEPHALIC LOBES AND BRAIN. 
The earliest stages of the eyes and optic ganglia are found 
before the appendages have made their appearance. The distal 
edge of each cephalic lobe is thickened to form the semicircular 
optic plate, distinguished on surface views by its opacity and the 
small size of its nuclei. The large ectoderm cells, on the inner 
