350 MOSTLY MAMMALS 



guarded with the same care ; the male not unfrequently 

 stirring up the eggs with his snout, and often keeping up 

 a fan-like movement of his fins for the apparent purpose 

 of ensuring a continual change of the water. 



As nest-building fishes are comparatively rare, much 

 interest attached to an account in the American Naturalist, 

 by Messrs. Young & Cole, of the manner in which the 

 brook-lamprey (Lampetra wilderi) makes a structure of this 

 nature. It is believed that the males precede the females 

 at spawning time and commence nest-building before the 

 arrival of the latter. The nest is made among pebbles, but 

 it does not seem that the lampreys follow any definite plan 

 in its construction. They affix themselves to such pebbles 

 as require removing from the nest, and then endeavour to 

 swim straight away with them. In the case of a heavy stone 

 two lampreys may join forces. The number of fish in a 

 nest may vary from one to thirty or forty; but there are 

 generally between three and twenty-five. 



Even when no nest is built, the males of some fishes mount 

 guard over the eggs ; this being the case with the bow-fin 

 (Amia calva\ so abundant in the lakes of North America. 



Such are some of the chief instances among amphibians 

 and fishes where special arrangements either of structure 

 or of habit are made for the protection of the eggs and 

 young; and although these bear but a small proportion to 

 the cases where the latter are left to themselves, yet they 

 are sufficient to show that in these respects these two 

 groups present peculiarities almost or quite unknown among 

 other vertebrates. Why such special arrangements have 

 been evolved in these cases, or whether the groups in which 

 they occur have any advantage in the struggle for existence 

 over their fellows, are questions which, for the present at 

 least, must remain unanswered 



