534, TRANSACTIONS OF SECTION D. 
Cranchiidz 
Liocranchia sp. ; . Chun (8) : ; . Ventral aspect of eyes. 
Cranchia sp. . ; . Chun (8) : : . Ventral and dorsal aspect of 
eyes. 
Leachia cyclura . . Joubin (26), Chun (8) . Ventral aspect of eyes. 
Leachia eschscholtzi . Chun (8) A . “ 4 3 
Taonius pavo . : . Chun (8) : c ¢ + a 9 
Desmoteuthis hyperborea . Chun (8) 
Corynomma speculator . Chun (8) 
Crystalloteuthis glacialis . Chun (8) 
Sandalops melancholicus . Chun (8) 
Toxeuma belone 5 . Chun (8) ” ” ” 
Taonidium suhmi? . . Chun (8) ” ” ” 
Bathothauma lyromma . Chun (8) 
From this table it would appear that luminous organs occur in the following 
situations :— 
1. Ventral surface of mantle. 
2. Ventral surface of body-wall within the mantle-cavity. 
3. Ventral surface of siphon. 
4, Ventral surface of head. : ; 
5. Ventral surface of arms (usually confined to the ventral and ventro-lateral, 
rarely found on the dorso-lateral, and very rarely on the dorsal). 
6. Ventral surface of eyeball. 
7. Ventral 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 existence 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 (32) of Hamburg, a pupil of Professor Chun. When working 
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 pro- 
perties. 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 trans- 
parent mantle with a pale-greenish light like that of glowworm. It appeared, 
further, that when the animal 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, furthermore, the light is only given off on powerful 
stimulation, as, for example, when the mantle is cut open. The structure of these 
organs has as yet been only very briefly described by their discoverer: they con- 
sist 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, 
