92 



LUCEllNAUI.?^ AND THEIR ALLIES. 



diminish the relative thickness fully one-half, within the anchors, and to a far 

 greater extent in the region of the passage-way [frj. 83, i') between the umbellar 



camera;. 



189. The Eye-spot.— \i two or three points (*\ I'it-lSO, 182) in the progress of 

 this memoir we have enlarged more or less npou tlie functional nature of the so- 

 called eye-spot. In addition to what has been already oft'ered we would draw 

 attention to the peculiar manner in which the pigment matter is disposed. We 

 find it holding exactly the same relation to the prismatic cells {fig. 83, 0), i. e., 

 formino- a dark casing or envelope about them, as the pigment does to the facets 

 of the eyes of Articulata. Adding to this the evidently special character of these 

 cells, as exhibited by their extreme elongation, and by their close aggregation and 

 prominence at a given point, we have all that can be brought forward in favor of 

 tlieir functional characters as elements of an optical apparatus. Although we 

 are not eager to assert tliat they are capable of forming distinct images of sur- 

 rounding objects, we are, on tlie contrary, far from denying that they may possi- 

 bly be capable of acting as refractive agents ; since every cell that possesses a con- 

 vex contour is a fraction of a lens ; and a combination of such cells as we have 

 here may constitute a whole lens in effect. It may not be luiadvisable to state 

 here that we hold, with others, that, notwithstanding the so-called eye of an insect 

 is a compound of many single eyes, it none the less is functionnU// an ojitical 'indt 

 so for as its effects upon the optic nerve is concerned; producing, like the pair of 

 human eyes, but a single image on the brain, 



§ 24. Young, ./^ of an Inch Across. (PI. iii, figs. 26, 27, 28.) 



190. Tlic Anchors and Eije-spots. — There is but one feature of tliis phase that 

 our illustrations are intended for, and that is the condition of tlie coUelocystophores 

 or anchors. The prehensile portion (oc'^) of these bodies has been described in a 

 previous section (§ 22) with considerable fulness, and therefore needs no further 

 notice here, but the so-called ci/e-spot ((;) remains yet to be considered, although it 

 has also been touched upon in preceding paragraphs (^ 127, 189). We have 

 nothing in the way of details to add to wliat was given in regard to the preceding 

 phase (^[ 189), but we may say a word or two more in reference to the latest con- 

 dition in which this organ has been observed. It now attracts the attention of the 

 observer by its distinctly marked outline, deep color, and particularly by its boss- 

 like prominence {fig. 26, 0). It is remarkable for appearing to be possessed of 

 a lens imbedded in its middle ; but this is a fallacy arising from the more abundant 

 accumulation of pigment granules in the periphery of the eye-spot than at the 

 centre, and hence a comparatively clear area is left in its midst. After this period 

 the eye-spot is gradually lost sight of ; but still we cannot say positively that its 

 functional character is obliterated, for we are not sure that it is possessed of such 

 at any time; and it may possibly retain all its potential features, even when, in 

 extreme old age, it is obscured, to the eye of the observer, by the abundance of 

 diffused pigment spots all around it. 



