624 P. W. GAMBLE AND F. W. KBEBLE. 



exposed to this light, and many recovered to their diurnal 

 tints, but several were still quite blue and transparent when 

 recorded again in a white porcelain dish in the laboratory. 



II. November 22nd, 1898. Mr. Andrew Scott (Curator 

 of the Piel Laboratory), working during a very low tide on an 

 exposed bank called the " Scar " at 5.30 a.m., observed that 

 the prawns in the tide-pools were brown, green, and pink. 

 The morning though dark was starlight ; the moon, being in 

 her first quarter, shed little light. 



III. December 15th, 1898. On the Scar from 6 to 7.30 

 p.m. Very low ebb. Night clear, calm, and starlight. The 

 Hippolyte collected in the pools consisted of nocturnes and 

 " diurnes " in about equal proportions, while those trawled in 

 two feet or so of water on the outer side of the bank were all 

 full nocturnes. 



IV. December 16th, 1898. On the Scar by 6.30 a.m. 

 Very dark thick weather, calm with misty rain. Poor ebb^ 

 only a small portion of the bank showing above water. All 

 specimens obtained by hand-nets in the pools and among the 

 weeds were nocturnes (some transparent and colourless). 

 Dawn commenced about 7, and by this time some of the 

 Hippolyte showed partial recovery to their diurnal tints. 

 As it grew lighter the proportion of these increased, until at 

 7.30 to 7.45 none but fully recovered specimens were to be 

 found. 



These facts establish the conclusions that the transparent 

 and usually blue nocturnal condition of Hippolyte varians 

 is due to a normal and nightly change, that the change 

 occurs while the prawns are still on their beds of weed, that 

 the twilight before daybreak may be sufiicient to induce a 

 recovery of the diurnal colour in prawns occurring close to 

 the surface of the water, and that the recovery is usually to be 

 associated with the dawn, and gradually affects those indi- 

 viduals which may be a few feet below the surface. 



Hippolyte varians is not the only Crustacean in which 

 we have discovered such a nocturnal change. In the same 

 hauls which contained several nocturnes of this prawn we have 



