NUDIBRANCHIATA OF THE L.M.B.C. DISTRICT. 151 
(Pleuronectes platessa), a few small thornback rays (Raza 
clavata), turbot (Rhombus maximus), and one brill (Rhombus 
levis), and on one occasion had some young cod (Gadus 
morrhua). The average size of these flat fish is six or 
seven inches in length, and there are over sixty of them 
altogether in the tank. 
C is an octagonal centre or table tank with a sandy 
bottom, measuring 4 feet 6 inches in diameter and 17 
inches in depth, and holding about 100 gallons of water. 
It contains various small fishes, viz., bullhead (Cottus 
bubalis), wrasse or goldsinny (Ctenolabrus rupestris), pogge 
(Agonus cataphractus), gemmeous dragonet (Callionymus 
lyra), five-bearded rockling (Motella mustela), viper weever 
(Trachinus vipera), and young cod (Gadus morrhua). 
All these fishes were in a thoroughly healthy condition, 
and some of them had been living undisturbed in their 
tanks for periods varying up to four years. The water in 
the tanks is kept aerated, and in constant circulation by 
a water engine. ‘The fish are usually fed upon mussels, 
cockles, and occasionally worms, which are thrown in at 
the top of the tank and allowed to sink slowly through the 
water. Such food matters are usually seen at once and 
eagerly pounced upon and eaten during their descent. We 
adopted the same plan in putting most of the nudibranchs 
into the tanks; and as, in anticipation of the visit to the 
Aquarium in the afternoon, the fishes were not fed on the 
days we intended to experiment with them, they had been 
fasting for about twenty-four hours, and so may be regarded 
as being unusually eager to seize any object dropped into 
the water. At the beginning, and again at the end of each 
day’s experiments, we threw a couple of cockles or mussels 
into the tank, and found that they were at once caught 
and bolted in the usual manner. 
