(U^ >IK. STAXLKY KKMP ON THE [^I'l'- 1^> 



is not more strongly cliitiniseil than the rest of the exoskeleton. 

 Both portions are quite transparent in material preserved in weak 

 formalin. A veiy delicate investing membrane possibly occurs 

 on the outer side of the lens, but its presence could not be demon- 

 strated clearly in any of the sections ol)tained. 



Situated immediately behind the lens and exceeding it in 

 diameter is the first cellular layer. This is composed of a number 

 of large wedge shaped cells which apjjear to be dei'ived from the 

 epithelium ; from eight to ten are .seen in a median section of 

 the organ. They are all full of protoplasm and their nuclei 

 invariably lie close up again.st the lens. In matei-ial pieserved in 

 formalin this Inyer is seen to he im])regnated with a deep blue 

 pigment. 



The second cellular layer is extremely inconspicuous ; it consists 

 merely of a few flattened nuclei round the outside of the first 

 layer. 



The tliii-d layer Hansen very reasonably considers to be a 

 reflectoi-. In material preserved in formalin it is of a distinctly 

 yellow coloiu' ; it is faintly striated and contains numerous peju*- 

 shaped nuclei which are very regularly arranged with their narrow 

 apices directed towards the lens. 



The fourth and last layer consists of a number of iiregularly 

 disposed cells i-ound the back of the reflector. It is possible that 

 in life these cari'ied a pigment, but in the preserved specimens 

 no trace of this remains. 



In some instances a neiwe-strand commiuiicating with the 

 photophore was detected, but the exact mode of its entrance could 

 not be discovered. It is not improbable that it runs lound the 

 edges of the reflector and then turns inwards to supply the first 

 cellular layer, in much the same w^y as has been demonstrated 

 liy Chun in the photophores of Euphausians. 



One of the two organs placed on the underside of the eye.stalk 

 is situated in closest proximity to the cornea. In this case 

 (PI. LIV. fig. 2) the photophore is slightly twi.sted and is 

 directed forwards and downwards. It is shut ofi" f rom the cornea 

 l)y a layer of black jngment, and its nerve-supply is not drawn 

 from any of the optic ganglia, but from a separate .stiand which 

 runs up the inferior margin of the stalk. 



It will be noticed from PI. LIU. figs. 2, 3, that the lens 

 may difier considerably in convexity, and in one case (fig. 4) 

 it is plano-convex. This photophore is placed at the base of the 

 exopod of the first niaxillipede and is directed forwards ; as 

 Hansen mentions, it is partially, though TU)t entirely, overhung by 

 the surrounding tissues. 



In neither of the two species is anything known of the develop- 

 ment. The photx>phores, hoAvever, difi'cr slightly in numlter in 

 the examples which I have exiimined, and it is probable that, as 

 in tlie ca.se of Acontlicjihi/ra dchlUs, they continue to increa.se as 

 the .specimen gains in size. Additional oigans seem to appear 

 long after the individual has attained matvnitv. 



