1910.] PllOTOPnORES OF DECAPOU CRUSTACEA. C)45 



photopliores on the pleopods, but their arrangement is not so 

 reguhir, and thongh the majority of the nuclei are placed near 

 the lens this is by no means the case with all. The cells show a 

 tendency to converge towards a point, but no granules similar to 

 those in the othei' photopliores were detected. In some sections 

 a. nerve-strand may be seen leading away fi'om the organ and 

 passing between two muscle-bands. 



Other spots and streaks of dark blue pigment to the number of 

 133 are found in adult examples of A. deh'dis. They occur on 

 the eyestalks, on certain legs, on the branchiostegites and other 

 parts of the carapace, on the abdominal segments and on the 

 telson. With the exception of a small number, which occur on 

 the dorsal aspect of the cai'apace, abdomen and telson, all are 

 situated laterally or ventrally. 



Coutiore, while fully realizing that little or no structural 

 evidence could be advanced in favour of such a theory, has no 

 hesitation in ascribing a luminous function to tlie cells under- 

 lying these pigment- spots. With this view I fully concur, and, 

 as will be seen later on, I am able to bring forward another fact 

 which supports this inter])i'etation. 



In the only passage in which he i-emarks on the anatomical 

 chai'acters of the organs, Coutiere * says : " Les organes lumineux 

 de la base des pleopodesparaissent se rapprocher beaxicoup deceux 

 des Euphausidfe, tons les autres semblent etre de simples amas de 

 cellules a lumiere, disposees sur une seule assi.se et recouvertes de 

 pigment." With the latter part of this sentence I am in entire 

 agreement. In numerous sections, made through all the more 

 prominent spots of pigment, the underlying cellular layer pre.sents 

 no visible difference from that of the adjacent tissue. To this 

 thei'e is only one exception : a section cut transversely through 

 the telson near the apex (PI, LIII. fig. 1) shows that the cells 

 beneath the dorsal spot of pigment are greatly elongated, though 

 their nuclei differ in position from those found in the more 

 elaborate organs. 



The brilliant scarlet-red pigment, which is such a notable 

 characteristic of many deep-sea Decapods, presents featiu-es of 

 special interest in the case of Acanthephyra dehilis, for it is quite 

 undeveloped in the neighboui-hood of the luminous organs. This 

 is particulaily well shown in the case of the photopliores at the 

 base of the pleopods. "Viewed laterally, these organs would be 

 quite invisible, being wholly covei-ed by the flaps foi'med by the 

 abdominal pleui-a, were it not that in these pai'ts the red pigment 

 is entirely absent, leaving the transparent cuticle thi'ough which 

 the light emitted by the photophore may shine as through a 

 window. The luminous streaks behind the last pair of thoracic 

 legs are covered by the branchiostegal wall of the cai-apace, and 

 in these a precisely similar phenomenon may be observed. 



Red pigment is also absent from the vicinity of all the numerous 



* Loc. cit. 19015, p. 1, footnote. 



