Gasterosteus aculeatus and G. spinachia. 245 



the spawn was frequently examined by the parent, who would 

 occasionally seize hold of it and give it a good shake ; appa- 

 rently for the purpose of throwing off adherent matter, that the 

 water might freely circulate about the eggs. The parent would 

 then dive, head foremost, into the nest and bring out a mouth- 

 ful of mud, which it would carry to some little distance and 

 discharge with a puff. 



The third day was passed much in the same manner, only as 

 the eggs were now all hatched, the nest was less frequently 

 fanned or ventilated ; and the fry, about forty in number, were 

 allowed greater liberty; the strongest being permitted to re- 

 create themselves among the Confervse that grew on a stone 

 about 2 inches from the nest. On the fourth day the fanning 

 had ceased altogether, and the rambles of the young were less 

 restricted. They were not yet, however, permitted to pass be- 

 yond certain limits ; when any transgressed these bounds they 

 were immediately seized, as heretofore, and carried back to the 

 nest ; into which they were always veiy glad to escape from the 

 clutches of their ardent parent. Notwithstanding all her vigi- 

 lance, one contrived, on the fifth day, to escape her eye, and pass- 

 ing the fatal boundary was immediately devoured by the other 

 fish, which now seemed always on the watch, neglecting its own 

 barren nest, being intent only on appropriating to itself the 

 nestlings of its fruitful neighbour. In this act of cannibalism 

 we see the reason for the parent's anxious care and its jealousness 

 of its kind ; and it is evident from Mr. Crookenden's account, 

 previously quoted, that they greedily devour each other's spawn. 

 The young fry, however, have other enemies as well as their own 

 species. One day a favourite Hydra [H.fusca) was observed to 

 be distended in a most extraordinary manner; on examination 

 it was found to have swallowed the head and shoulders of one of 

 the young fish many times larger than itself ; and the caudal 

 extremity, which was too much for it, and which was projecting 

 out of its mouth, had been seized upon by another Hydra. Thus, 

 it would appear that these low organized, but powerful and vo- 

 racious animals occasionally regale themselves on the flesh of the 

 Vertebrata. This happened when the fry were three or four 

 weeks old. 



All the old fish, with the exception of that with the young, 

 were, in consequence of their cannibal propensities, turned out 

 of the trough ; and danger being thus removed, the fry were no 

 longer restricted in their rambles, but enjoyed the whole range 

 of their crystal abode. Henceforth the parent's assiduity gra- 

 dually relaxed, though for days afterwards it was its custom to 

 take the young occasionally into its mouth, and after carrying 

 them a Uttle distance to let them drop out again. I took one of 



