456 Miscellaneous. 



and easy of investigation, which subsequently become soldered toge- 

 ther, indistinct, and unfit for investigation. Each of the divisions of 

 the eye corresponding with a facet of the cornea is formed by a cer- 

 tain number of perfectly definite cells, of which the greater part are 

 arranged in fours. Thus in the Peacock Butterfly (Vanessa Io) 

 there are seventeen cells, of which sixteen are in fours. These cells 

 are arranged in the following manner. Four of them form a globular 

 mass, flattened at its upper part, which is adherent to the cornea ; 

 these are the four cells which secrete the corresponding facet of the 

 cornea, which proves, like all chitinous membranes, to be an extra- 

 cellular production. The four nuclei of these cells are still easily re- 

 cognized in the adult, in which they are adherent to the cornea. Each 

 of these cells secretes in its interior a very refractive globule, which 

 is nothing but the rudiment of one quarter of the crystalline body. In 

 fact, this body, which is single in the adult, is always (in all Insects 

 and Crustacea) composed originally of four distinct parts, which sub- 

 sequently become united. After these four cells come four others, 

 forming a pyriform mass. This is the rudiment of the nervous 

 baton, which will afterwards attain much greater dimensions, at a 

 period when it will be no longer possible to recognize the four cells 

 composing it, although its production at the expense of these four 

 cells is still indicated by the four-sided prismatic form which it pre- 

 sents in the adult. The point of the pyriform mass rests upon a 

 large single cell, which the author calls the fundamental cell (Grund- 

 selle), because it forms the base of the eye properly so called. This 

 cell itself is placed at the extremity of a nervous filament arising 

 from the optic ganglion, and the nine cells form the axis of the optical 

 element corresponding with a single facet. The other eight are 

 destined subsequently to become its enveloping coat. Four of them 

 are placed in the constriction which separates the mass in which the 

 four quarters of the crystalline body are formed from the pyriform 

 mass placed below it ; the others in that separating the pyriform 

 mass from the fundamental cell. During evolution the former always 

 become filled with a pigment, the colour of which, in many species, 

 is different from that of the pigment deposited at the same time in 

 the top of the nervous baton. 



Sometimes the number of cells composing the optical element is 

 much greater, but this multiplication affects exclusively the cells of 

 the enveloping coat. This takes place, for example, in JSschna 

 grandis, in which the number of cells of the envelopes properly so 

 called is raised from four to thirty-two, and the pigment-cells are 

 also greatly increased in number. 



In a physiological point of view, the author shows that the theory 

 of vision in the Arthropoda, as established by Miiller, cannot be sus- 

 tained, however ingenious it may be. In fact, if this theory were 

 well founded, those insects which have only a small number of facets 

 in the cornea (such as the Ants, which have only fifty) would be 

 utterly incapable of perceiving images. Even those which have 

 the greatest number would be extremely short-sighted ; and M. Cla- 

 parede calculates that a Bee would be unable to discern the opening 



