August 29. 1907] 



NA rURE 



455 



negative I called their special attention to it, and offered a 

 handsome reward for the next specimen secured, either 

 alive or in good condition, and then passed on to other 

 fishermen and repeated my promise. Shortly afterwards 

 I was summoned and shown a specimen clinging to the 

 net, which I seized and placed in a vessel of water. At 

 that moment I enjoyed the astonishing spectacle of the 

 brilliant spots, which appeared upon the skin of this animal, 

 whose remark-able form had already impressed me : some- 

 times it was a ray of sapphire blue which blinded me ; 

 sometimes of opalescent topaz yellow, which rendered it 

 still more striking ; at other times these two rich colours 

 mingled their magnificent rays. During the night these 

 opalescent spots emitted a phosphorescent brilliance which 

 rendered this mollusc one of the most splendid of Nature's 

 products. Its existence was, however, of short dur.ntion, 

 though I had placed it in a large vessel of water. Prob- 

 ably it lives at great depths." 



The species thus referred to was Histioteuthis boiiellianci, 

 which we shall have occasion to refer to in the sequel. 



The next observation, so far as I am aware, was made 

 by Prof. Chun, on board the Valdivia during the Ger- 

 man deep-sea expedition, on a form which he has called 

 Thaumatolampas diailciua. The specimen captured lived 

 long enough to allow of a photograph being made of it 

 whilst in a state of functional activity, and the appearance 

 it presented is thus described by the observer : 



" .\mong all the marvels of coloration which the animals 

 of the deep sea exhibited to us nothing can be even dis- 

 tantlv compared with the hues of these organs. One would 

 think that the body was adorned with a diadem of brilliant 

 gems. The middle organs of the eyes shone with ultra- 

 marine-blue, the lateral ones with a pearly sheen. Those 

 towards the front of the lower surface of the body gave out 

 a rubv-red light, while those behind were snow-white or 

 pearly, except the median one, which was sky-blue. It was 

 indeed a glorious spectacle." 



Finally we have the genera Heterotetithis and Si'piola, 

 the phosphorescent properties of which were seen last year 

 by Dr. W. T. Meyer and Dr. W. Marchand in the 

 Zoological Station at Naples. 



This short list comprises all the actual observations on 

 the luminosity of these animals ; in these, however, the 

 photogenic function has been definitely associated with 

 special organs, and it is by comparison with these that 

 other organs in other species have been regarded as having 

 the same significance. 



The history of the anatomical examination of these organs 

 dates back only to the early 'nineties, and, so far as I can 

 ascertain, the right of priority of the discovery rests with 

 Prof. Joubin, who made a communication to the Soci^t^ 

 scientifique et medicale de I'Ouest at Rennes on Februar)' ^. 

 iSg'j, a brief account of which was published by the Soci^t^ 

 de Biologic of Paris on the lolh of the same month : this 

 communication related to Histioteuthis ruppelli, and in it 

 attention was called to \'erany's observation quoted above. 

 Sections of the organs of Ahraliopsis were exhibited at the 

 Gottingen meeting of the German Zoological Society and 

 at the NottinghaiTi meeting of this Association in the 

 same year. Successive memoirs by Joubin and others 

 followed, and in 1903 Prof. Chun delivered an address 

 to the German Zoological Society at Wiirzburg, in which 

 he gave a masterly survey of the whole subject, brought 

 forward instances of similar organs previously overlooked, 

 and showed the great variety in structure, not only in the 

 organs of different species, but even in organs of one and 

 the same individual. 



More or less adequately authenticated luminous organs 

 have now been recorded in no fewer than thirty-three 

 species of Cephalopoda, and they have been found to occur 

 in the following situations : 



(i) Ventral surface of mantle. 



(2) Ventral surface of body-wall within the mantle- 

 cavity. 



fj) Ventral surface of siphon. 



(4) Ventral surface of head. 



(i) Ventral surface of arms (usually confined to the ven- 

 tral and ventro-lateral, rarely found on the dorso-lateral, 

 and very rarely on the dorsal). 



NO. 1974, VOL. 76] 



(6) Ventral surface of eyeball. 



(7) \'entral surface of tentacles. 



(8) Dorsal aspect of the dorsal arms. 



(9) Dorsal surface of fin. 



The most striking fact apparent from this summary is 

 that luminous organs are practically confined to the ventral 

 aspect of the animal. Another remarkable fact is the exist- 

 ence of organs concealed beneath the mantle and beneath 

 the integument covering the eyeball, which can only be 

 effective by reason of the transparence of the tissues in the 

 living creature. 



To give a detailed description of the structure of these 

 many and varied organs would be out of place on the 

 present occasion ; it must suffice to group them into more 

 or less well-defined classes and take an example from each. 



The luminous organs of Cephalopoda may be divided in 

 the first instance into 



A. Glandular. 



B. Non-glandular. 



A. Glandular Organs. — In this class we have to deal only 

 with the type of structure found in Heteroteuthis, Sepiola, 

 and Rossia, which has been investigated by Dr. W. T. 

 Meyer, of Hamburg, a pupil of Prof. Chun. When work- 

 ing at the Naples Zoological Station he was fortunate 

 enough to obtain a specimen of Heteroteuthis dispar, and 

 Dr. Lo Bianco called his attention to its luminous proper- 

 ties. On examination in a dark room it was easy to see 

 the organ lying on the ventral surface of the body, just 

 behind the funnel, showing through the transparent mantle 

 with a pale greenish light like that of the glowworm. It ap- 

 peared, further, that when the aniinal was irritated it shot 

 rapidly through the water, leaving behind it a trail of 

 luminous secretion which floated in the form of separate 

 globules, and were afterwards drawn out by the currents 

 into long threads. Dr. Meyer was able to repeat this 

 exhibition of fireworks several times. 



In Sepiola the luminous secretion is not ejected, but 

 remains attached to the surface of the gland ; and, further- 

 more, the light is only given off on powerful stimulation, 

 as, for example, when the mantle is cut open. The struc- 

 ture of these organs has as yet been only very briefly 

 described by their discoverer : they consist of paired glands, 

 situated as above described one on either side of the anus, 

 and partially concealed by the lateral margin of the ink- 

 sac, which forms a recess for their reception. Beneath 

 and to the inner side of the gland there is a reflector, and 

 above it is a rounded gelatinous mass, fibrous in structure, 

 transparent during life, covered with a delicate muscular 

 layer. Dr. Meyer hesitates as to the function of this mass : 

 biit I think, in view of the structure of the luminous organs 

 in other species, we may hazard the suggestion that it is 

 some kind of lens. This organ is of particular interest, 

 because it is the only instance yet recorded of a luminous 

 organ among the Myopsida and the only glandular luminous 

 organ in the Cephalopoda. Glandular luminous organs 

 are, however, known in many species of fish, and in Pholas 

 among the Molluscn. 



B. Non-glandular Organs. — These may perhaps be divided 

 into 



(i.) Simple, without special optical apparatus, 

 (ii.) Complex, with more or fewer of the following 

 structures : pigment layer, reflector, lens, dia- 

 phragm. 



(i.) ."Vs a type of the simpler kind we may take the 

 branchial organ of Pterygioleuthis giardi, in which w-e 

 have a central mass of parenchymatous tissue, with a deli- 

 cate superficial membrane (consisting of two thin la^jers), 

 and resting upon a rather thick layer of close, compact 

 tissue, which stains very deeply ; beneath this organ is a 

 single layer of cells containing a reddish-brown pigment. 

 The corresponding organ in the nearly allied Pyroteuthis (or 

 Pterygioleuthis) margaritifera is a degree more complex, 

 for underneath the central cell mass is a thick layer 

 of scale-like bodies, similar in structure to that regarded in 

 other cases as a reflector (" tapetum " of Chun). In both 

 these cases it seems necessary to regard the central cells 

 as the source of light (see Fig. .a). 



.Another organ, almost equally simple, is that found in 

 the tentacles of Thaumatolampas, where the central por- 



