60 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
into little linear groups of four to seven organs, separated by interspaces about 
equal in length to the groups. 
On the third pair (Plate 8, Fig. 2) there are little linear groups of two to 
six organs on the ventral surface along the line where the web or swimming 
membrane is attached to the arm. 
There are no organs on the fin. 
GENERAL APPEARANCE. 
Under a lens the luminous organs of the mantle, arms, etc., present the ap- 
pearance of small spots which are sometimes raised into papillae by the con- 
traction of the intervening integument (Plate 10, Fig. 3). They have a 
shining appearance and consist of a central white speck surrounded by a black 
ring. Under a low power of the microscope, the black ring is not quite even, 
but has a wavy external margin and in some cases is clearly seen to be made 
up of from five to seven separate pieces; this is still more clearly seen to be 
the case when sections are examined. 
The white central portion presents a somewhat different appearance in dif- 
ferent organs. In the largest ones it has a yellowish tinge and is more prom- 
inent and looks harder than in others, In the organs of smaller size it is paler 
and flatter, being of a dull pearly white color. In the smallest of all it is 
quite flat, and in these, too, the pigment ring is much less developed. 
The diameter of one of the largest is about 0.2 mm., the central pearl-like 
spot being about 0.1 mm. in diameter. They vary considerably in size, the 
smallest being about half as big as the largest, They lie in spaces between 
the chromatophores. 
MINUTE STRUCTURE. 
The preparation of complete series of sections of these organs was found to 
be quite impossible, owing to the hardness of the posterior part of the interior. 
The cutting went on quite satisfactorily until about halfway through, when 
the whole of the remainder of the inside was torn out by the razor, generally 
spoiling the adjacent tissues on one side and damaging all the remaining sec- 
tions of that particular organ. In what follows the account of the posterior 
part has been compiled from a few very indifferent fragments. 
The organ lies embedded in the fibrous connective tissues under the epi- 
dermis and is below the level of the chromatophores with which it does not 
seem to come into any relation. There is a slight depression in the sub- 
cutaneous muscle underneath each organ. There is a series of large sinuses 
surrounding the posterior portion of the organ (Figs. 4 to 8, s.). The inner 
wall of these is formed by a thin layer of connective tissue surrounding the 
pigment cup, whilst the outer is formed by the sub-cutaneous connective 
tissue. : 
The shape is in general spheroidal, the axial diameter, perpendicular to the 
surface of the integument, being rather longer than the transverse diameter. 
