640 MR. STANLEY KKMP OX THE [Apr. 19, 



Their true function was fir.st tlenionstrateJ by 8ai\s *, and their 

 structure is now well known owing to the work of Chun f and of 

 Vallentin :ind Cunningham j. 



Photophorcs occur only in three genera of Decapoda, all of 

 which belong to the Macnu'a, or, according to niodeiii systems of 

 classitic-ation, to the Natnntia. One of them, Seryestes, belongs 

 to the Penieidea, and the other two, Acaiithephi/ra and Hoplo- 

 phorus, to the Oaridea. Although, as might be expected, two 

 Avliolly different types of structure are found in these two groups, 

 they have none the less one very striking feature in common — in 

 both a deep blue pigment is associated with the luminous organ. 

 This pigmentation is one of the most interesting characteristics 

 of the photophores of Decapoda, for, except for the fact that it 

 has once been observed in a Euphausian, such an association 

 appears to be elsewhere unknown. 



The following six species of Decapods possess photophores : — 



Pen/eidea. 



8ergestid?e Seryeates chaUenyeri Hansen , 



iSeryestes yloriosiis tStebbing. 



Cauidea. 



Hoplophorida^ ... Acanthep/ii/rn pelliicida Perrier. 



Acanthep/i>/ra debilis A. Milne-Edwards. 

 HnpJojihoras yrlinaldii Coutiere. 

 Hoploplionis: sp. juv. 



Two other genera, (rennadas and AuKdoppuceus. belonging to 

 the family Pena^ida', may also possess photophores, but it has not 

 as yet been possil)le to come to any definite conclusion on the 

 subject. 



The material which I have been able to examine consists of 

 one species of each of the three genera mentioneil above. I am 

 indebted to Prof. J. >Stanley Gardiner for the opportunity of 

 examining four sjjeoimens of Seryestes cliallenyerl and an immature 

 Hoplophorus from the Indian Ocean. The examples of the former 

 genus are presei'ved in formalin and have in consecpience retained 

 some at least of their original pigmentation. Acanthephijra debilis 

 occurs in all stages off the West coast of Ireland. This species is 

 unfortunately far from common, and although special efforts have 

 been made, no fresh material has been found during the last 

 eighteen months. In consequence, it ha.s not been po.ssible to 

 solve certain problems connected with the pigmentation and in- 

 nervation of the photophoies. 



Deep-.sea Decapods ai'e almost invaiiably dead wlu-n brought 

 to the surface, and although in view of recent investigations it 

 does not .seem probalile that the vitality of the organism has 



* Siirs, Report mi tlir ' ('linllcii;rcr " Sclii/oipoilii, ISSo, ]i. 70. 

 + Chun. HiMi..tli<M-a Zooloi^ica, M. vii. (Heft 10). iH'.Mi. )). 191. 

 X Vnllciiliii it Ciiiiiiiiifrlumv, Q. .1. Miiv. Sci. xxvwi. 188H, p. 319. 



