290 ANATOMY. 



The form, situation, number, and external differences of the eyes of 

 insects, have been already sufficiently described in the first division of 

 our present inquiry ; we can therefore presume that all these points are 

 known, and proceed at once to its internal structure. Upon turning a 

 preliminary glance to the history of the progress of these observations, 

 we shall find all the earlier investigations unsatisfactory. The facets 

 in the eyes of different insects were numbered, the optic nerve and its 

 radial branches were also known, and a distinction was made between 

 compound and simple eyes, without the peculiar structure of the latter 

 being detected. After such, upon the whole unsatisfactory, preludatory 

 labours*, Marcel de Serres f undertook a more comprehensive investi- 

 gation of the eyes of insects, in which he, indeed, discovered much that 

 was new, but was far from exhausting the subject, which is evident 

 from the subsequent labours of Joh. Muller $. It was reserved to this 

 indefatigable inquirer to give a comprehensible explanation of the eyes 

 of insects, and to lay the foundation of the correct doctrine of the sight 

 of insects with both compound and simple eyes. The following is the 

 result of his admirable investigation, confirmed by Duges, in opposition 

 to Straus-Durkheim ||. 



The simple eyes of insects agree entirely in structure with the eyes 

 of the superior animals, particularly of the fish. It is found in all the 

 larvae of insects with a perfect metamorphosis, and in many families of 

 perfect insects of all orders. The following Table will give a more 

 precise survey. 



I. Insects with merely simple eyes. 



. The larvae of Coleoptera, Lepidoptera, Hymenoptera, Neurop- 

 tera, and Diptera (with the exception of Culex and the ap- 

 proximate water larvae, which possess compound eyes). 



6. TheDicfyoioptera, Thysanoura (with the exception of Machilia 

 and Mallophaga}. 



II. Insects with simple and compound eyes. 



a. The majority of insects with an imperfect metamorphosis, 

 consequently. 



* Consult Schelver Versuch einer Naturgeschichte der Sinneswerkzeuge bei den 

 Insekten. Getting. 1798. 8vo. 



t" M6m. sur les Yeux composes, et les Yeux liss^s des Insectes. Montp. 1813. 8vo. 



\ Zur Vergleichende Physiologic des Gesichtssinnes. Leip. 1826. 8vo., and Suppt. to 

 it, in Meckel's Archiv. 1828. 



Annales des Sc. Nat. xx. 341. 6. || Ih. torn, xviii. p. 463. 



