The Eye of By b lis scrrata. 



40 



lens shows no stratification. But tlie great and important differences are 

 that the eye of Ampelisca has no humor space, lacks the middle layer of 

 the eye of Byblis, wliile the latter possesses pigment, middle layer, and 

 finid-filled space. 



Details of Histological Elements op the Eye. 



Lens. —The lens is about the same size in each of the four eyes. Its out- 

 line is almost exactly circular in a surface view, and the curvature of the 

 superficial and deep surfaces is nearly the same. Fig. -4, len. The lens, 

 which is only a modification of the cuticula, shows even more plainly 

 tlian the latter its com- 

 position of successive 

 layers, the markings be- 

 ing as is commonly the 

 case in lenses which are 

 strongly convex, more or 

 less concentric. 



Lenligen. — There are 

 three distinct layers be- 

 neath the lens, whicli in 

 passing from the surface 

 to the deeper portions I 

 shall call respectively len- 

 tigen, middle layer, and 

 retina. The lentigen con- 

 sists of a single layer of 

 elongated ceils which ra- 

 diate more or less regu- 

 larly from the lens as a 

 center, Fig. 4, I. They 

 are of unequal lengths, 

 those of tlie center being 

 longest, and those nearer 

 the margins of the lens 

 successively shorter, so 

 that the deep surface of 

 the lentigen is usually 

 hemisi>herical with a 



tendency to a conical form. The transition to the unmodified hypo- 

 dermis is nevertheless quite abrupt. The nuclei of the lentigen cells are 

 closely crowded in a single layer at the deep surface of the lentigen — often 

 so closely that they are nearly twice as long as broad They are granuhu 

 and have distinct nuclear membranes. The hypodermis underlying the 

 cuticula that surrounds the lens is filled with roughly spherical granules 

 of pigment. The hypodermal cells form a single layer of epithelium, but 

 ^he pigment obscures this structure to such an extent that it is almost 

 mpossible to make out the cell boundaries. In some sections, where 



Fi(i. 4. — Diugraniniatio section of right vyr. ol' |i(]ste 

 rior pair, slightly ohliquely transverse to cliiof axis of 

 body : Icn, lens ; I, lentigen ; h, hyporlermis ; s, space ; 

 .<■, middle layer of cells ; r, rods; c, cones; ret., reti- 

 nute; nil, nuclear region of retina. X 350. 



