BETINA OF THE BLOWFLY. 



407 



From that day to this I have continued to work at the subject, 

 and T 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. 1 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 unanimitj'^ 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, Yiallanes, 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 pap)er 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 ' " {I. c. page 27). 



Even the most cursory acquaintance with the work of the 

 German naturalist would have shown Dr. Hickson that this is 

 an egregious misstatement of Dr. Weismann' s nomenclature. 



