648 MR. STAXLEV KEMP ON THE ['^V^'- ^^t 



Acuiilhepk>/ra, but from tlie fjict tliat it tuni.s red when l)<)ileil or 

 wlieii treated with sti-ong acids it is very pi-obahU; that it is of 

 the same nature. 



The existence of l)lue coloration in deep-sea animals is ex- 

 ceedingly rare, and its occurrence among Dec.ipoda in close 

 as.sociation with the i)hi)tophores is almost uni(|ue, for among the 

 Euphausiacea a similar pigment appears to have heen noticed only 

 on a single occ^asion. In Xovemlier, 1901), a large specimen of 

 'J7ii/s(tiioj)0(Ia acntifrons Holt tt Tatter.sall was caught in a mid- 

 water net ofi' the West coast of Ireland. This specimen, which 

 was dead by the time it reached the deck, was found to possess 

 patches of deep blue pigment associated with the jihotophores on 

 the eyestalks. Casual examination failed to reveal this pigment 

 in the othei- photophores, which, liowever, were of a darker colour 

 than is usually the case. The specimen was put aside in a di.sh of 

 water and when it was again exn mined, not more than half an ho\ir 

 later, all trace of the blue pigment had vani.shed. It is eviilent 

 that, even if in this case the blue coloin-ing invaiiably occiu's in 

 the photophores, the phenomenon is one of great rarity among 

 Euphausians, for it certainly is not found in Meganyctiphanes 

 norve(/ica or in any of the conunon N. Atlantic .species. 



The blue pigment of the photophores of Decapoda is much 

 more stable than that noticed in 2'. acutifrons. Although r;ipidly 

 extracted by alcohol, it will persist for years in specimens preserved 

 in weak formalin, remaining distinct long after the general red 

 colouring has disappeared. 



The lens of Acmithephj/)-a,heing blue, can necessarily only allow 

 the emission of blue light and it is not impo.ssible that this is 

 also true in the case of tSeryestes, where tlie leTis is transparent 

 and the first cellular layer blue. It seems then that, at least in 

 the former genus, the production of blue light is a necessity, 

 but it is impo.ssible to suggest any ex])lanation of this curious 

 phenomenon. 



Photophores have evidently been develojied 1)y Crustacea in at 

 lea.st three separate instances. Those po.sse.'^sed by Acanthcplij/ra 

 and Ifoplophorus are in structure wholly distinct from those of 

 tSeryesles, while in neither case is there any reseml)lance to the 

 very complex oi-gaiis of the Eujdiausiacea. 



It is a. ren)arkable fact that, whereas in the latter order the 

 ]K)s.session of jihotophore.s is the general rule (only in JientheU' 

 phansia are they absent), their occurrence in large genera such as 

 St'vijestps and Acanthephyra'M^ limited to a few species only. This 

 is particularly noteworthy in Sercjestes, in which two forms, both 

 of which are cla.s.sed among a small group of extremely clo.sely 

 allied species, exhibit a large nunibei' of photophores, whereas 

 none are to be found in the other membei-s cfmiposing tlie group. 



J)otlein, in a .shoi-t but interesting paper*, h;is summarised the 



* Dnflpiii, Sit/.uiig-lici'. il. (ji'b. r. Mdipliol. mill I'lnsiol. \u .Miiiicln'ii. .wii. 10117. 

 PI'. 13'J 136. 



