W. C. M'Intosh on the Abyssal Theory of Light. 5 



night or by day in a darkened room or recess ; and this feature 

 of itself would raise a doubt as to such having any connexion 

 physiologically with the capture of prey or of being conspi- 

 cuous to marauders. 



The free gonozooids of many of the Hydroid zoophytes, 

 therefore, and the true Medusse are pelagic and phosphorescent 

 animals, whose active life is passed at or near the surface of 

 the water, so that they can scarcely be included under the 

 head of abyssal inhabitants, though some descend during 

 quiescence to the bottom. We have no proof that the lumi- 

 nosity of such forms occurs only at night ; for, as before men- 

 tioned, I have found various species, like the annelids and the 

 Coleopterous larva recently described by Dr. H. Burmeister*, ex- 

 hibit this property as vividly during the day as during the night, 

 if taken into a suitable place for observation, and without 

 any previous seclusion in darkness as described by Dr. Allman 

 in Beroe. Medusse, besides, do not, so far as I know, form a 

 common food of other marine animals in our seas (their most 

 notable enemies, perhaps, in this respect being each other), 

 and their habits and structure do not point to their exercising 

 the luminosity for the sake of seizing their prey. Moreover 

 there does not seem to exist the provision mentioned in the 

 report, whereby, in virtue of their lessened phosphorescence, 

 the breeding individuals are preserved. There is nothing in 

 the history of Pennatula or Pavonaria which would lead us to 

 infer such interpretations of their luminosity ; and though the 

 former sometimes occurs in the stomach of the cod, it must be 

 borne in mind that inconspicuous mollusks and annelids are 

 at least as common, not to mention stones and iron nails. 



Phosphorescence could be of little service to the brilliant 

 Pyrosoma in capturing prey ; and, to balance the fancy that 

 this was given for the sake of attracting plunderers, we have 

 the fact that the allied and equally palatable Salpge of the 

 British waters are not luminous. 



It is asserted that the young of the starfishes emit more 

 light than the adults in order that they may the more readily 

 court destruction ; but it may be asked, are the young of the 

 Hydroid Zoophytes, of Beroe, or the young Annelida more 

 luminous than the adults ? Apparently not ; and in some cases 

 rather the reverse. Further, we may inquire as to the facts 

 bearing on this question in those starfishes which are not phos- 

 phorescent. The structure of the group and their habits in 

 feeding, again, show that such illumination could only be of 

 service to their enemies. But we have no reliable data to 



* Pioc. Linn. Soc. (Zool.), vol. xi. no. 54, p. 419. 



