211 



NOTES AND MEMORANDA. 



Notes on the Senses and Habits of some Crustacea. — In tlie course of 

 investigations as to the perceptions of fishes, some interesting facts 

 in the natural history of Crustacea have come under my notice. All 

 the Crustacea in the .tanks, except Carcinus moenas and Portunus 

 depurator are more active by night than by day. Prawns, Pandalus, 

 Stenorhynchus and Inachus generally remain stationary during the 

 day, but will leave their places to hunt for food if any be put in ; 

 but Ebalia, Portunus 'pusillus, Porcellana longicornis, Galafhea 

 andreivsii, Virhius varians and shrimps are rarely visible until 

 night falls, and hardly ever come out by day even to feed. Eury- 

 nome aspera, though not hidden away like these, being naturally 

 almost indistinguishable from the broken shells, &c., amongst which 

 it lives, seems also never to feed by day. Excepting the shrimps, 

 nearly each individual of the above-mentioned forms has its own 

 place to which it retires when morning comes, and in which it 

 remains during the whole day. One prawn has occupied the same 

 hole for some weeks, and another, which had lived a fortnight 

 in one corner, left it when some mussels were put iu, and now 

 sits on the mussels during the day. The distinction then between 

 day and night is of importance to these animals. Such an animal 

 as a shrimp is in fact certain to be caught by keen-sighted fishes if 

 it uncovers itself by day. If shrimps are thrown by day among 

 pollock, they are always eaten unless they reach the bottom of the 

 tank, but there they are safe even if uuburied, for the pollock seems 

 unable to see them when on the bottom, and at once gives up the 

 chase. This may or may not be due to their protective colouration. 

 Pollock very rarely take anything off the bottom, and worms and 

 even glistening things like pieces of mackerel are generally left by 

 them if they are not eaten whilst sinking,* Moreover, the bottom 

 of the pollocks' tank is made of yellow gravel brought from the 

 Chesil Beach, which in no wise resembles a shrimp. 



Wrasses, however, which are especially fond of shrimps, can not 

 only catch them as they sink in the water, but pursue them on the 

 bottom. The sight of the wrasse is particularly keen, and I have 

 often seen a large wrasse search the sand for shrimps, turning side- 

 ways and looking with either eye independently like a chamasleon. 

 Its vision is so good that it can see a shrimp with certainty when the 



• This can only be true of small pollock, for large pollock are frequently taken with 

 ground baits. 



