62 LIFE-HISTORY AND DEVELOPMENT OF 



an intimate connection between them and the hordes of jelly- 

 fishes {Aurelia and Cyanea) which abound in the inshore 

 waters towards the end of summer. He thought the young 

 cod approached the jelly-fish for the sake of the minute pelagic 

 animals stupefied by its poisonous threads, and that the fish 

 repaid this favour by picking off a parasitic crustacean (Hyperia 

 medusarum) which clings to the jelly-fish. Observations, con- 

 tinued for a long period in this country, however, show that 

 this connection is only casual and of very little importance, and 

 that certain Hyperice are occasionally found in vast numbers in 

 a free condition. 



As the season advances, the young cod are joined off the 

 rocky ledges by a few pollack and whiting, but not by the 

 haddock, which has certain social views of its own — keeping to 

 the deep water farther out. The size of these cod late in autumn, 

 as in October, varies, some reaching from 4 to 5 inches in 

 length. Their food ranges from zoophytes to crustaceans, 

 mollusks, and small fishes, and in confinement the larger are 

 voracious, an example in the laboratory about 5 inches readily 

 attacking a smaller (3 inches) and swallowing it as far as 

 possible, though for some time a considerable portion of the 

 body and tail of the prey projected from the mouth. Moreover, 

 the tessellated condition becomes less marked, and as they 

 approach 8 inches in length a tendency in some to uniformit}' 

 of tint is noticeable. Many of those, however, that continue to 

 haunt the rocky shores and the tangle-forests beyond low water 

 still retain for some time mottled sides, and they are known by 

 the name of rock-cod. Further, while their growth in the 

 earlier stages is less marked, it is now very rapid — even in 

 confinement. The exact rate of growth in the free condition in 

 the sea is difficult to estimate, but the little cod of an inch and 

 a half to an inch and three-quarters in June reach lengths 

 varying from 3 to 5 inches in autumn, and in the tanks of the 

 laboratory, specimens 5 inches in August attain 8 inches the 

 following March. At Arendal, in Norway, where opportunities 

 for watching the growth of cod in confinement have been 

 supplied with a liberality not excelled in our country, Capt. 

 Dannevig found that the cod of 3 mm. in April reached onlj' 



