80 PRELIMINAKY EXPERIMENTS ON 



prey. A moribund Blenny larva was placed in a watch-glass of sea- 

 water with a number of the Copepods, and kept under observation 

 under the microscope for twenty minutes. The larva was still capable 

 of spasmodic darts. The Copepods occasionally settled, on the larva, 

 but usually left it at once, even when the latter made no signs of 

 objection to their presence. If they remained, and began to feed, the 

 larva would shake them off by wriggling away, though sometimes with 

 difficulty if the Copepod was tenacious. Twelve Copepods visited the 

 larva during the time. Of these, seven left at once, three very soon, 

 and two after being shaken off by the larva. At the end of twenty 

 minutes the moribund larva was removed, and a corpse offered to the 

 same Copepods. In the same time nine Copepods visited the corpse. 

 Of these only three left at once, while the other six remained to feed, 

 some for five minutes, but the majority for the remainder of the experi- 

 ment. The moribund larva was now weaker ; the heart was beating, 

 but the respiratory movements had ceased. It could no longer shake off 

 the Copepods, and these remained to feed precisely as on the corpse. 



The above experiments indicate that these carnivorous Copepods, 

 especially Idija furcata, prefer dead prey, but do not hesitate to attack 

 living fishes or larvae on occasions. Although even Blenny larva? could 

 probably free themselves of these pests under ordinary circumstances, 

 the extraordinary accumulation of the Copepods in my rearing tank 

 appears to have subjected the larvae to such incessant attacks from 

 them that they were unable to cope with them, and finally gave way, 

 especially as the second lot of larvre appears to have been rendered 

 temporarily torpid from the beginning by the change from the plunger- 

 jar to the tank — a condition which would reduce their ability to drive 

 off the pests. 



I made one further experiment which may provide a useful means of 

 preventing the accumulation of these Copepods in aquaria. A small 

 Wrasse {Ctenolabrus rupestris), 2 inches long, was introduced into the 

 tank when the Copepods were literally teeming within it. Next morn- 

 ing the Wrasse was very lively, and the Copepods were exceedingly 

 scarce. On watching further, I saw the Wrasse busily engaged picking 

 them off the slate walls one by one with unvarying exactitude. Its 

 stomach on dissection was found to be filled with the Copepods. 



The result of this instructive accident in my second rearing experi- 

 ment was that the two larva? which still survived in the slate tank were 

 again transferred to a plunger-jar as before ; and in this they continued 

 to thrive for another month without further incidents calling for notice. 

 They completed their metamorphosis, and one survived to become a 

 sturdy little fish an inch in length, with the entire organisation and 

 habits of the adult, even to the extent of making a house for itself out 



