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to the mode of development as set forth by Dr. E. Claparede. More- 

 over, as in many cases these cells become so fused as to form an 

 entirely homogeneous body, the author thinks that the single 

 crystalline lens, possessing many nerve-bulbs (as in mollusks), is 

 formed really by the combination of their various lenses ; the pig- 

 ment in this case being confined to the nerve-bulb, which is its 

 normal position. 



It is then pointed out, for the first time, that in some insects, and 

 in lulus, the lens possesses a very slight refractive power, being filled 

 with a fluid as little refractive as water. This is more particularly 

 the case in the Diptera, where the dermal facets become so spherical 

 as to usurp the function of the lens, while an example is furnished 

 by the eye of Aromia moschata of the complete disappearance of the 

 lens. In opposition to the opinion entertained by many naturalists, 

 the author maintains that each bulb, provided with a refracting body, 

 is capable of perceiving a picture independently of the assistance of 

 other adjoining lenses. 



The homology of the nerve-sheath is traced from its condition as 

 a delicate membrane which passes over the simple eye, to that of the 

 sclerotic and cornea ; and it is shown to constitute the true cornea. 

 After referring to the pigment and iris, the author discusses the 

 parts added to the simple eye. The anterior chamber, or the space 

 found anteriorly to the lens and iris (where the latter exists), first 

 appears in the leeches, but is a very variable element in the Inver- 

 tebrata, existing in some aquatic animals, as leeches and cephalous 

 mollusks, while it is absent in others, as Paludina, Limncea, &c. ; 

 and thus the opinion held by some, that an anterior chamber is of 

 little use in aquatic animals, as in fishes, is scarcely tenable, because 

 they have a compensation in the globular lens. The author has 

 never found an anterior chamber in the compound eyes of the In- 

 secta, although a space has been described, and erroneously called a 

 lens. Still the possibility of such a space is not thereby denied ; 

 only, should it exist, it would be homologous to the anterior chamber, 

 and not to the lens ; and the transparent body behind it is the true 

 lens, and not a vitreous humour, as is often represented. There is 

 such a chamber in the Decapods, in which it is well marked. In 

 regard to a chamber posterior to the lens, the author is of opinion 

 that none is to be found below the mollusks, and points out that what 



