536 TRANSACTIONS OF SECTION D. 
portion is conical, and also composed of concentric lamellx. Partly in front of 
and partly behind the diaphragm is a lenticular mass of tissue. These little 
lanterns are scattered in considerable numbers over the ventral surface of the 
mantle, funnel, head, and arms, and the appearance of the animal when they are 
functionally active must be brilliant in the extreme (see fig. c). 
If we examine the organs just described and the others above enumerated we 
see that certain conditions are fulfilled in all cases—namely, the presence of a 
mass of deeply staining, active cells with distinct nuclei, supplied with blood 
Semi-diagrammatic Sections of Typical Luminous Organs :— 
A. Branchial organs of Pterygioteuthis giardi. 
B, Tentacular organs of Thaumatolampas. 
C. Pallial organ of A braliopsis. 
D. Pallial organ of Histioteuthis riippelli.' 
a. Accessory tentacular organ. n. Nerve. 
ch. Chromatophores. p. Pigment. 
d. Diaphragm. ph. Photogenic cells. 
Z, Lens. ph'. Photogenic cells of accessory organ. 
la. Lacuna. 7. Reflector (internal). 
m. Mirror (external), 
vessels and nerves. These, then, are the essential parts of the apparatus, though 
even here differences obtain: for example, in Thawmatolampas the cells are poly- 
hedral, highly refractile, and clearly defined, with spherical nuclei and distinct 
nucleoli. In Chiroteuthopsis the cells are few and large, and partially fuse one 
with another. In Pterygioteuthis the fusion has proceeded so far that the cell- 
boundaries are no longer recognisable, and there is present a finely granular mass 
in which numerous nuclei of varying size may be distinguished. In other cases 
the cells branch out into fibres and form a reticulate structure (Callitenthis). In rare 
cases, as, for instance, the tentacular organ of Thaumatolampas, above described 
