642 F. W. GA]\[BLL] AND 1'. W. KEKBLE. 



may profouudly modify the colour ; aud tliougli we do not 

 presuDie to say how these difficulties can be overcome, we 

 would point out how small a value colour-records possess, 

 when made without these precautions. 



Indeed, the existing records seem to show that colour- 

 changes may occur during the ascent of the trawl. Not a 

 few of the Crustacea figured by Milne-Edwards during the 

 " Talisman " expedition show the red in patches on a more 

 transparent ground. Another good case we quote from 

 Prof. Gr. 0. Sars. In describing the Crustacea of the Nor- 

 wegian Xorth- Atlantic expedition the author refers (p. 32) 

 toBythocaris leucopsis, a prawn allied to Hippolyte. 

 The colour is a '' magnificent rosy red, a trifle more intense 

 at the end of each segment of the posterior division of the 

 body. Extending across the middle of the carapace is ob- 

 served, moreover, a large irregular saddle-shaped area of 

 a dark bluish colour. Again, the " Albatross " brought up 

 a prawn, Benthesicymus Tanneri, from eight hundred 

 aud sixty fathoms, which showed a considerable amount of 

 blue colour ; and Professor Faxon, in reporting on the pecu- 

 liar spottiness of the colour, makes the suggestion " that the 

 unique coloration of the deep sea prawn may be due to a 

 change of colour undergone by the animal as it was brought 

 up into the full blaze of day" (loc. cit., p. 255). 



Conclusions. — During the night, Hippolyte variaus 

 exhibits a condition markedly different from that shown 

 during the day. The most striking feature of the nightly 

 condition is the colour (nocturne) ; though other peculiari- 

 ties, such as the state of nervous irritability and the in- 

 creased I'ate of heart-beat, accompany the colour-change.^ 

 The complete colour-cycle, from diurnal phase to nocturnal 

 aud back again, is completed in about twenty-four hours. 

 Experiments in which the animals are subject to constant 

 light, as well as those in which they are kept in constant 

 darkness, show that the change is periodic ; that is, it 



' OUier changes ia tlie muscular system aud digestive-gland, accompany 

 tlie nocturnal phase. 



