RETINA OF THE BLOWFLY. 
407 
.From that day to this I have continued to work at the subject, 
and I now venture to bring before this Society evidence which I 
think can hardly fail to convince even the most sceptical of my 
opponents. Although I never had any doubt of the correctness 
of my figures or descriptions, I felt it incumbent upon me to 
produce preparations which would admit of no double interpre- 
tation, but which would appeal at once to the eyes of those who 
are only partially acquainted with the histology of the vertebrate 
retina. 
At the time I published my former paper I felt so certain that 
the views I held would receive a ready acceptance, that I did not, 
perhaps, enter sufficiently into minute details, and left many points 
to be investigated by other workers. I have since examined 
every structure in the greatest detail, and have much to add with 
regard to the developmental history of the compound eye. 
The retinal rods, which I figured correctly in my former paper, 
correspond with the periopticon of Dr. Hickson, except that his 
figures show that every vestige of nerve-structure and nerve- 
terminal organs had been completely destroyed in his prepara- 
tions, leaving nothing but the skeletal framework with the 
tracheal vessels, which he has delineated most carefully and 
correctly. 
He states that my paper and investigations were unnecessary, 
owing to the unanimity of previous investigators : none, however, 
agree in any detail with Dr. Hickson, nor, so far as I am able 
to judge, to any considerable extent with each other. 
Putting aside for the moment the earlier observers, the so- 
called periopticon of Hickson has only been described in detail 
by Berger, Carriere, Ciaccio, Viallanes, Hickson, and myself. 
To show how far these observers agree with each other and 
with the older writers, I will quote a few sentences from 
Dr. Hickson’s paper. He says : — 
“ Previous to the publication of Berger’s paper the optic tract 
of insects had been briefly described and names given to the 
various regions. Thus Weismann called the opticon and epiopti- 
con the ‘ bulbus,’ the region where the optic fibrils decussate the 
‘ Stiel,’ and the periopticon the ‘Augenscheibe ’ ” ( l . c. page 27). 
Even the most cursory acquaintance with the work of the 
Herman naturalist would have shown Dr. Hickson that this is 
an egregious misstatement of Dr. Weismaun’s nomenclature. 
