2 HOYLE, Pterygiotetithis margaritifera. 



I am not aware that any investigation has hitherto been 

 made into the structure of the luminous organs in this 

 species, and as I have recently been fortunate enough to 

 become possessed of a specimen it has appeared worth 

 while to give a brief account of the main features of their 

 organisation. The example at my disposal unfortunately 

 was not in very good condition, so that the observations 

 here recorded will doubtless require extension and correc- 

 tion when more suitable material is available. 



The luminous organs of this cephalopod may be 

 divided into four sets : — 

 I. Ocular. 

 II. Siphonal. 



III. Branchial. 



IV. Abdominal. 



I. The Oailar Organs form a series of warts projecting 



Fig. I. 



Sketch of the ventral aspect showing the position of the 

 luminous organs ; natural size. The mouth cavity and siphon 

 have been laid open and the integument covering the eye has 

 been reflected on the right side : a /—J, abdominal ; /';■ , 

 branchial ; o 4—g, ocular ; s., siphonal organs. 



