442 THE ZOOLOGIST. 



average weight of the three individuals of 21 mm. was 5*6 gr.* ; 

 the average weight of the three individuals of 23 mm. was 

 8*0 gr. ; the weight of those of 27 mm. was 12'7 gr. ; the weight 

 of the individual of 39 mm. (which was dead before the records 

 were actually begun) was not taken. The Sea-Urchins were 

 placed in an aquarium which stood in a fairly dark spot (lighted 

 when necessary by an electric lamp above). This tank held 

 nearly thirty gallons of well-aerated and gently-circulating sea- 

 water, which as far as possible was maintained of a uniform 

 salinity throughout the investigations. The floor of the aquarium 

 was covered to a depth of about an inch and a half with small 

 pebbles t; and the tank contained scattered rocks, seaweed, living 

 gastropods (Nassa reticulata, Purpura lapillus, Murex erinaceus, 

 Trochus cinerarius, and Littorina littorea), empty shells of these 

 gastropods, several Sabella, and about twenty individuals of the 

 Starfish known as Asterina gibbosa. The Sea-Urchins were well 

 fed with raw beef and seaweeds, and were plentifully supplied 

 with the broken shells and echinoderm skeletons which the Sea- 

 Urchins eat in considerable quantities. 



The aquarium was searched every morning (excluding Sun- 

 days), and any Sea-Urchin which was found to be carrying 

 materials picked up since the last examination was removed from 

 the tank, and the animal and the materials were weighed in a 

 small vessel of sea-water. The observations were carried on for 

 thirteen weeks, but as the results obtained were always of the same 

 general character, it seems unnecessary to present more than a 

 portioD of the records made. During the first twenty-eight conse- 

 cutive days (from June 30th to July 27th inclusive) eighty records 

 of the kinds and weights of objects carried were registered, and 

 these are as follows : — 



* The individuals of 21 mm. were so much alike that it was difficult to 

 distinguish between them, and the same remarks apply to those of 23 and 

 27 mm. The weights of all the Sea-Urchins differed slightly at different 

 times. Average weights have therefore been given in all cases. 



f If the convenient standards introduced by E. J. Allen (" On the Fauna 

 and Bottom-deposits near the 30-fathom line, &c," 'Jour. Mar. Biol. Assoc.,' 

 vol. 5, N.S.. 1897-9, pp. 365-542) are used, most of these stones would come 

 under the head of "medium gravel " and " coarse gravel." Allen describes 

 as coarse gravel the stones which are left in a sieve with holes of 5 mm., and 

 as medium gravel those which are left in a sieve with holes of 2*5 mm. 

 (p. 378). 



