•CKl'KI.OIDS. 



921 



trimsforination and dissolution of tlie gland-cells, whicli 

 lire aftei'wards ejected through that end of the tiilic 

 which ojieiis into the hollow. 



l-"roui this coni]iarative]y simple structure, which 

 as \et reminds us i)f slime-glands of I lie skin, the tirsi 

 step to higher differentiation is that, as the sac deepens 

 more and more, its inner (Ixittom) part is separated by 

 a consti'iction of the wall and liecomes spherical in 

 shape, while the nuter part remains more or less re- 

 ■■■ularh' cu|)-sliaped. a rotation-paraboloid with cir- 

 cular mouth, in which case tlic axis is \crtical di the 

 surface of the bod\- (tig. 281), or elliptical and more 

 or less elongated", in wliich case the axis is obliipudy 

 set. Throughout the wall of the organ, within the 

 layer of jjigment, lies an extremely thin, but power- 

 t'ullc retractive mendDrane (ni), which even extends over 



the mouth of the organ, where we also find a double 

 membrane, consisting of an inner, cellular leaf (c/) and 

 an outer, structureless one (r) explained as a kind of 

 lens, and situated within the thin, structureless epi- 

 dermis {li), which has been compared to a cornea. The 

 internal structure is otherwise essentially the same as 

 in the simjiler luminous spots — though both connective 

 tissue and nei'vous elements enter more plentifulK- into 

 its composition — but the shining mass (k) here lies 

 as a more or less lens-shaped body in the annular 

 constriction between tlie splierical (irmei') and cup- 

 shaped jiarts of the organ, forming a, disk Itetween 

 these two parts but itself di\ided into two parts (Ic 

 and 1) by a thin nuMubrane, which is distended like 

 a diaphragm right in the constriction. To this disk 

 run the exti-eme randhcations of the spinal nei've (ii) 



^0^^'-"lf^-^ 





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/HS5,ii 



:y^T^ira;- 





/ 



Fig. 231. A: Section of n coinpomiil liiininous spot in Antronesthes uiyev, X lOU. After Lendenfeld. 

 4, cornea-liiie, transparent part of sliin over the organ: c. transparent njcnilirane outside tlie lens-shaped body d; e, gland-tnbes of the sphe- 

 rical part; /, pigment layers: g and g' , pigment coating of the outer and inner parts of the luminons body; li, gland-tubes in the outer part 

 of the luminous body; k. granular mass and cells, inner part; /, outer part: m. shining membrane within the pigment layer; n, nervous cells. 



Fig 231. B: I'iagrammatic section of the luminous spot represented in fig. A, showing the rellection and refraction of the rays 



of light in the luminous spot. After Lendenfelp. 



"i — 0, and i] — b^, rays of light emitted from the central part {<■) of the luminous spot and reflected in the lower, spherical part of the 



same; c^ — Cj, </, — d^, f, — e,, and /, — f^, rays of light from the same source, emitted in a centrifugal direction, reflected from the sides of 



the outer, parabolic portion of the organ, and refracted by passing through the cornea-like layer (j/); ,rj?,, axis of the optical system; 



g, cornea; /(, shining tissue of the outer, parabolic part; i, glands of the inner, spherical part. 



" See for example the upper spois in our figure of Argyropeleciis Olfersii. 



