ATLANT. DEEP-SEA EXPED. 1910. VOL. III]. 



CEPHALOPODA. 



19 



1 can only with some reserve venture to give an 

 explanation of this structure. Without entering into hazy 

 suppositions I will only point out that it first of all 

 presents a certain likeness to a light-organ, the shell 

 representing the reflector and the ball-shaped agglomera- 

 tion of cells filling its aperture corresponding to the 

 luminous body. 



We may further mention that slender and transparent 

 cirri alternate with the suckers or with their stalks, the 

 longest of these cirri measuring about 7 mm. Besides 

 this peculiar development of the arm suckers, which is 

 unique among all known Cephalopoda, I may point to 

 another equally surprising feature in the organisation of 

 Cirrothauma, viz. that Cirrothauma is the only blind 

 cephalopod known. I have already mentioned that 

 the eye, situated between the second and third arms, is 

 strikingly small, being only 3 mm diameter. It does not 

 protrude, and a closer scrutiny proves it to be devoid of 

 a lens. Seeing behind the eye, in the deep layers of 

 the gelatinous mass, a second dark body, I decided to 

 make a preparation of the entire structure, subsequently 

 cutting it in sections. In this paper I will not enter into 

 a detailed description but refer the reader to fig. 10, 

 which illustrates the appearance of the isolated eye. 



It is first of all striking that the eye as already stated 

 is entirely buried in the jelly of the gelatinous body, the 

 outer point of the eye being specially coated with a thick 

 layer. The eye-bulb is almost bali-shaped, only a little 

 flattened in front, devoid of pigment in the anterior third 

 part, the rest being of a deep violet colour. The anterior 

 border of the pigment is somewhat irregular, extending a 

 little farther on the ventral side. The bulb is surrounded 

 by a light-coloured space (a), representing the outer water- 

 filled chamber of the eye. It is perfectly closed, and no 

 trace of an opening is visible in our perfect specimen. 

 This chamber overlaps the bulb behind, terminating in a 

 ringshaped thickening, which perhaps may be explained 

 as being homologous to the white body (alb.). The bulb 

 is strangely thin in front and only a little thickened behind 

 in the pigmented part. Above all the entire absence of a 

 lens is confirmed, a fact noticeable on a merely superficial 

 survey. Connected with this is the absence of a ciliary 

 body and iris. The posterior side of the bulb is surrounded 

 by gelatinous tissues, through the centre of which, as will 

 presently be shown in detail, the optic nerve passes. 



Behind the eye is located an almost equally large 

 and also light violet coloured body (s. ven.), as previously 

 mentioned. This body somewhat approaches the main 

 axis of the animal, being of an irregular bullet-like shape, 

 bulging a little behind. A large vein (v. ophth.) enters 

 into this body, being presumably homologous to the v. 

 ophthalmica of the normal cephalopod eye. The latter 



forms, as I have specially observed in Bolitaena, an 

 enormous sinus around the optic ganglion. At first sight 

 one might get the impression that the entire dark body 

 represented an optic ganglion, but the sections show that 

 very peculiar conditions are present, the body representing 

 an enormous venal sac, densely filled with blood corpusc- 

 les. It is the latter which actually produce the dark 



ophth. 



•opt. 



'-ophth. s. 



••■v. ophth. 



Fig. 10. Rudimentary eye of Cirrothauma. 



a. External space surrounding the bulb. alb. White body. 



opth. i. Nervus ophthalmicus inferior, ophth. s. Nervus 



ophthalmicus superior, opt. Nervus opticus, sin. v. Sinus 



venosus. v. ophth. Vena ophthalmica. 



colouring, and might easily induce anybody not familiar 

 with the actual conditions to believe that one had to do 

 with an optic ganglion filled with minute ganglion cells. 

 If we penetrate still deeper, the yellowish brain 

 becomes faintly visible, sending 3 fine nerves towards 

 the bulb. The middle one of these is the optic nerve 

 (opt.), which is not actually rudimentary, but very thin 

 compared with the optic nerve of other Cephalopoda. 

 It runs right through the dark sinus venosus without 

 forming any thickening which might be explained as the 

 ganglion pedunculi. Between the sin. venosus and the 

 bulb a faint knot-like swelling is noticeable, being possibly 

 a rudimentary ganglion of the optic nerve. Single strands 

 run from the latter place to the bulb. The difference from 

 normal conditions is quite obvious. The optic ganglion 



