No. 6. The Eyes in Scorpions. By G. H. PARKER.* 
THE subject discussed in the following pages has already attracted the 
attention of able investigators, and were it not that the authors of the 
later papers have pointed out questions only partially answered, a recon- 
sideration of the subject might appear presumptuous. It is hoped that, 
in discussing these questions from an embryological as well as histological 
standpoint, the additional evidence obtained may throw some light on 
their solution. 
The study of the eyes in Arthropods requires so much technical skill 
that until very recently satisfactory work in this field has been almost 
impossible. Aside from papers mainly of historical interest, the most 
comprehensive publication for the student to-day is Grenacher’s ‘‘ Unter- 
suchungen iiber das Sehorgan der Arthropoden.” This appeared in 1879, 
and contained an admirable study of the eyes in spiders; it did not, 
however, touch upon the organs of sight in scorpions. The same year, 
Graber, in his paper entitled “‘ Ueber das unicorneale Tracheaten- 
Auge,” severely criticised Grenacher’s conclusions. Grenacher, in order 
to answer his critic, turned his attention to the eyes in scorpions, and, in 
his paper on the eyes in Myriapods, published in 1880, he included a 
reply to Graber. Three years later a comparison of the eyes in the scor- 
pion and king-crab was published by Lankester and Bourne. The sub- 
stance of these four papers, when viewed in the light of newly discovered 
embryological facts, has recently been fully discussed by Mark. Previous 
to the appearance of Mark’s paper, Patten, after having made a compara- 
tive study of the eyes in certain mollusks and arthropods, included in his 
general description an account of the histology of the eyes in scorpions. 
The five papers quoted, namely, those of Graber (’79), Grenacher (’80), 
Lankester and Bourne (’83), Patten (’86), and Mark (’87), are the only 
ones in which the histology of the eyes in scorpions is considered. 
The publications on the development of the eyes are even less exten- 
sive than those on the histology. Metschnikoff (’71, p. 225), in his 
* Contributions from the Embryological Laboratory of the Museum of Compara- 
tive Zoology at Harvard College, under the Direction of E. L. Mark. — No. XII. 
A Thesis presented for the Degree of S. B. 
VOL. XIII. — No. 6. 11 
