20 



CARL CHUN. 



[REP. OF THE "MICHAEL SARS" NORTH 



present in all Cephalopoda has been reduced to a faint 

 thickening of the optic nerve just behind the bulb, and 

 is entirely devoid of typical ganglion cells. Besides the 

 the optic nerve we further notice two nerves approaching 

 the surface of the bulb, branching in order to innervate 

 the feebly developed muscle-lamellae, which are situated 

 in the gelatinous tissues surrounding the eye. The dorsal 

 one of these nerves corresponds to the N. ophthalmicus 

 superior (ophth. s.), the ventral one corresponding to N. 

 ophthalmicus inferior ( ophth. i.). 



Our description would be imperfect if we omitted to 

 mention the layer, which we may consider as the retina 





M 



ri 



\\ 1/1 



%3 



Fig. 11. Retina of Cirrotliauma. 



f. Fibrous layer, pg. Retinal pigment, s. Sense cells. 



st. Scattered rods. 



(fig. 11). If we examine the pigmented part of the bulb 

 somewhat closer, we find that this pigment is composed 

 of two layers. The inner one of the layers coats the bulb 

 with a dark and thin continuous layer, the outer one 

 appearing on its periphery as isolated flakes or pigment 

 granules; the dark violet hue of the bulb is mainly due 

 to the latter. Behind the inner layer of pigment densely 

 located nuclei are visible, being roughly arranged in two 

 layers. They may possibly be considered as being the 

 nuclei of pigment cells as well as nuclei of the retina 

 cells. The degree of degeneration to which the eye has 

 been subjected is most strikingly shown by the condition 

 of the rods (st.). In all other Cephalopoda the latter are 

 densely crowded and firmly welded together, exhibiting 

 in transverse section the well known net-like structure. 

 In our specimen however, they are widely separated from 

 each other. They are strangely short and generally a 

 little pointed at the free end, projecting like minute flames 

 from the pigment-layer. 



If we survey the whole of the conditions described, 

 we recognise a reduction of the eye so far advanced, 

 that nothing similar is known in the Cephalopoda. Among 

 deep-sea Cephalopoda we certainly know forms with 

 comparatively small eyes, but the very structure of the 



eye is never involved in the reduction. In the present 

 case, however, we miss not only the dioptric apparatus, 

 the lens and the ciliary body which forms the latter, but 

 the optic nerve equally exhibits an extreme degeneration 

 hitherto unknown in Cephalopoda. The ganglion pedunculi 

 and the ganglion opticum are lacking, the white body 

 which I consider as identical with the ringshaped thick 

 ening (alb.) being also rudimentary. 



Finally, considering that the main layer of the retina 

 (the layer of the rods) also exhibits an excessive degenera- 

 tion, I think that I am justified in asserting— as I have 

 done— that Cirrothauma is the only blind cephalopod 

 known. The degeneration of the eye is much farther 

 advanced than in the case of many blind vertebrates. 

 Whether the development of light-organs in the gelatinous 

 stalks is correlated to the degeneration of the eyes can 

 only be settled if in future we should be lucky enough 

 to bring one of these wonderful organisms to the surface 

 alive and witness the organs mentioned by me actually 

 emitting phosphorescent light. 



In conclusion we may briefly discuss the question 

 of the bathymetrical distribution of the Cephalopoda, as 

 illustrated by the "Michael Sars" collections. In the first 

 place we may remark that certain forms live at the bottom, 

 having only been taken in the trawl. Typical denizens 

 of the deep-sea mud are found in the genus Oplstoteuthls 

 taken at depth of 923 m. I consider the closely related 

 Cirroteuthis umbellata only taken in the trawl in depths 

 of 2615 and 2055 m as a bottom dweller, and also the 

 large new Octopus lothel captured by the trawl in 1365 

 m. depth. 



All the other Cephalopoda taken by the expedition 

 are pelagic forms. As regards those among them which 

 evidently prefer deep water, we have generally to do with 

 rare guests represented usually by only a few specimens. 

 It is impossible accurately to define the level at which 

 they have actually been floating. During the cruise of 

 the "Valdivia" our general impression was that the pelagic 

 deep-sea Cephalopoda were either much rarer than the 

 pelagic deep-sea fishes, or that they were better able to 

 evade the nets. During the cruise of the "Michael Sars" 

 large closing nets were employed, and the vertical range 

 has been ascertained at least in the case of one species, 

 viz. Calllteuthis reversa, which was taken at Station 52 

 in a haul between 1200 and 1000 m. The other closing-net 

 hauls which yielded Cephalopoda were all made near the 

 surface, as follows: 



Stat. 10. 500—180 m. Desmoteuthis pelluclda, 2 

 young specimens. 

 „ 63. 500—200 m. Teuthowenia megalops, 1 

 specimen. 



