HOYLE : EEPOKTS ON THE CEPHALOPODA. 



APPENDIX. 



THE LUxMINOUS ORGANS OF CERTAIN CEPHALOPODA. 



(A) Pterygioteuthis giardi. 



(Plate 9.) 



The luminous organs in this species closely resemble, as might be expected, 

 those of the nearly allied species, Pyrotenthu margaritiftra. Of these a short 

 notice has recently appeared (Hoyle, : 02), and what follows will, of neces- 

 sity, be to some extent a recapitulation of that paper. The specimens which 

 came into my hands had not been preserved with any special view to his- 

 tological examination, and some of them had suffered a good deal of injury, 

 so that the account here given can only be regarded as of a preliminary 

 character. 



The most striking peculiarity in regard to the luminous organs in the genus 

 Pterygioteuthis is that they are situated on the eyeball or within the mantle- 

 cavity, in either case below the integument, so that they are only functional 

 by reason of its transparence during life. After immersion in alcohol the tis- 

 sues become opa([ue, and though sometimes one or two of the larger ocular 

 organs may be dimly seen through the skin, it is only after dissection that 

 they are clearly visible, or, in the case of the intrapallial organs, visible at all. 



As in the Mediterranean species, the luminous organs may be divided, 

 according to their situation, into four sets: — 



I. Ocular. 



II. Siphonal (Plate 9, Fig. 1, S., S.) 



III. Branchial (Fig. 1, B., B.) 



IV. Abdominal (Fig. 1, A\ A^). 



I. The Ocular Organs are disposed in the equatorial region of the ven- 

 tral aspect of the eyeball, and resemble a series of warts projecting from it. 

 Owing to the damaged condition of the eyes in most of the "Albatross" speci- 

 mens, I have been unable to determine their number and position with cer- 

 tainty, but there appear to be five, situated at approximately regular intervals 

 on the lower half of the equator of the ej'eball. Each organ is roughly sphe- 

 roidal, with the outer surface somewhat flattened and the deeper more convex. 

 The diameter and the depth are subequal, being about 0.45 ram. in the larger 

 and a little more than half as much in the smaller. 



