III. 



Observations on Certain Marine Animals. 



I. — A New Protective Device of Maia squinado. 

 II. — Colour Assimilation among Fishes. 

 III. — A Fighting Stratagem of the Crawfish {Palinurus). 

 IV. — Abnormalities in Halidystus (Lucernaria). 



I. — A New Protective Device of Maia squinado. 



I HAD occasion recently to watch closely the habits of the large 

 Spider Crab, Maia squinado, while in captivity in the Aquarium 

 tanks of the Jersey Biological Station. The first individual obtained, 

 a female, was temporarily placed in a large bare tank, unfurnished 

 with either boulders or sea-weeds. A thin layer of fine shingle 

 about an inch in depth covered the bottom. Maia for a while was 

 very restless, seeking, apparently, for a suitable place of concealment. 

 Finding none, she at length took up a position in the centre of the 

 tank, scratching a hollow in the shingle wherein to lie. After a short 

 interval of rest she began an admirable plan of concealment. First 

 with one chela and then with the other the crab selected and lifted 

 carefully pebble after pebble and deliberately, placed them, closely 

 fitted together, upon the surface of the carapace, the rough spinous 

 nature of this being admirably suited to hold them in position. 

 Rarely a pebble would fall off, so carefully did Maia poise them and 

 so steady did she hold her body. At the end of a quarter of an hour 

 the red spiny back was converted into a little mound of pebbles, and 

 the crab absolutely hidden. 



Now Maia, in common with several allied species, such as Pisa 

 tetraodon, Achats cranchii (Spence Bate Ann. and Mag. Nat. Hist., 

 1866), and Stenovhynchus, etc., has the habit of decorating and trim- 

 ming the carapace and limbs with scraps of weed hooked often quite 

 artistically on to the recurved bristles that beset these parts. This 

 with obvious protective intention. But Maia at home seems never to 

 frequent pebbly localities. Its habitat is in the sand and under the 

 weedy, root-matted edges of the Zostera banks. Hence it is reason- 

 ably to be inferred that the protective device described above was 

 independently thought out to meet the special exigencies of the 

 occasion. Several other Maia subsequently placed in the same tank 

 performed precisely the like operation. 



