1910.] PIIOTOniOR-JS OF DECAPOD CRUSTACEA. tU3 



A comparison of the foregoing description with the account 

 and figures whicii Hansen gives of the structure of these organs 

 reveals many discrepancies. There can be little doubt that this 

 is due to the fact that Hansen viewed the organs only in optical 

 section, a method which, even in his hands, has not yielded 

 satisfactory results. 



The Photophores of Acanthephyba. 



Two species of Acanthephyra are known to possess photophores. 

 They are first mentioned l)y Perrier in 1886* in a form Avhich he 

 cilled '■'■ Acanthephiira iiellnckla A. Milne-Edwards." There is 

 unfortunately a good deal of uncertainty I'egarding tlie validity 

 of this species, for it has not been rediscovered in recent years 

 and Milne-Edwards seems to have never published any descrip- 

 tion. Our knowledge of it is, in consequence, derived solely from 

 the brief refei-ence iw Perrier'.s work, and the accuracy of the 

 account of the distribution of the photophores, which is there 

 given, is by no means certain t. 



Acanihe'phyra debilis is better known. Coutiere in 1905 X 

 first described the existence of photophores in this sjiecies, and in 

 1906 § he published a moi-e complete account of their number 

 and distribution. 



The photophores in ui. debilis ai-e not all of similar structure, 

 as they ai-e in the case of Sergestes, but exist in different degrees 

 of complexity in different parts of the animal. 



The most highly developed organs are twelve in number, and 

 each is so placed that the liglit which it produces is thrown 

 directly downwards. One is situated on the distal and external 

 aspect of the protopodite of each pleopod, and one behind the 

 protopodite of each ui-opod. The structure of these photophores 

 is illustrated in PI. LII. fig. 1 and PI. LIY. fig. 1. 



Externally there is a thick concavo-convex || lens formed from 

 the cuticle. In adult specimens this measures about '24 mm. in 

 diameter, and during life is of a deep violet-blue colour. The 

 pigment does not exist as a mere coating, but permeates through- 

 out the structure of the lens. Sections stained with picro- 

 carmine show that the lens is made up of three distinct layers. 

 The inner and outer portions are merely thickenings of the two 

 cuticular layers which form the normal exoskeleton of Crustacea 

 and under a high power show the usiial striations. The middle 

 layer, which is also striated, always stnins moi'e deep!}' with carmine 

 than the others, and, owing to the fact that it sometimes takes 



* Pevrier, Les fxplorations sons-marinos, ISSfi. 



+ A comparative view of the positions occupied by the photo]ihores in A. pel- 

 lucida and in A. debilis will be found in Kemp, Fisheries, Ireland, Sci. Invest., 19u8, 

 1. ri9lO], p. 67. wliere Feri'iers original description is reprinted. 



t Covitiere, Bull. Mus. (_)ceanog. Monaco, no. 48. 190-5. p. 7. 



§ Coutiere. Bull. Mus. Oc^anog. Monaco, no. 70. 190fi, p. 4. 



ij In a few of the section? obtained the lens i^ plano-con\-ex, hut thir, I lielieve to 

 be due to distortion. 



