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 

 rin". 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. 



Tiie organ lies embedik-d in the fibrous connective tissues under the e]ii- 

 dermis and is bt-low the k-vel of the chromatophores with which it does not 

 seem to come into any relation. There is a sliglit 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 iimer 

 wall of these is formetl by a thin layer of connective tissue surrounding the 

 ]>igment cup, whilst the outer is formed by the sub-cutaneous connective 

 tissue. 



The shape is in general s]ilKToi(lal, the axial diameter, perpendicular to the 

 Burface of the iuteguntent, being rather longer than the transverse diameter. 



