a?id smooth or simple Eyes of Insects. 1 13 



slightly we look at them, we soon perceive an infinite number 

 of polygons, the centre of which appears to be white. All these 

 white points are the extremities of the nervous filaments coming 

 from the expansion of the grand optic nerve*, or from the re- 

 tina, and which have traversed the choroid and its coatiug. We 

 may convince ourselves of this in the following way: the brain 

 being laid bare, we may follow the optic nerve, a,nd see it di- 

 rected to the eye, where it spreads, and is divided into a multi- 

 tude of filaments. But if we draw these filaments, the white 

 points disappear completelv, and there only remain on the 

 coating, streaks variously coloured; which ]3roves that these white 

 points are the extremities of the nervous filiaments. We may re- 

 cognise this arrangement in the great species, such as the lihel- 

 liilcp, the tiuxaiw, and the common cricket. In the species 

 which have no streaks on the cornea, \\'& also observe on tlie 

 coating of the cornea, the furrows or ridges which form the 

 facets of this membrane, and the coating, which is more or less 

 deep, having the form of a polygon, which represents the facets 

 of the cornea. 



These retinae, peculiar to each facet, are those which Swam- 

 merdam has called the pyramidal of the eye. These compound 

 fibres, according to him, proceed to a membrane as to a com- 

 mon centre, and it is the circular trachea from which the fila- 

 ments issue : he also observes correctly, that it is through its sub- 

 stance that the trachea pass which ascend along the pyramidal 

 fibres. The figure of these fibres is hexagonal, and their upper 

 extremity is broader than their lower, spreading out a little, as it 

 would seem, when they get into the concavity of the cornea, and 

 taking the form of this membrane. 



To conclude: Swammerdam states that he never was able to 

 ascertain whether these fibres were muscvilar or nervous, al- 

 though it would have been easy to convince himself of it, since 

 they mav be followed to the brain. As to the transverse fibres 

 which Swammerdam has described f, I never perceived them. 

 I am led to tliink that this expert anatomist must have made 

 a transverse section in the eye and the brain, and that he formed 

 these fibres by the section which he made in the optic nerve. 

 At least, it is certain that these fibres commuijcate with the 

 brain, for Swammerdam himself admits it : he remarks even 

 that we might compare them to a very considerable nerve which 

 we observe in the furrow, which nerve derives its origin from 

 the brain. 



* We desif;nate the nerve which proceeds to the compound eyes, under 

 the name of grand optic nerve, in order to di'^tinguish it from the optic 

 nerves whicli proceed to the simple or smooth eyes. 



t Bibliu NutureE, tat), xx. fig. 5. 



Woh44. No. 196. August I8i4. H ^ In 



