104 SCIENCE SKETCHES. 
The Common Eel! is more or less regularly 
catadromous. It is doubtless of marine origin; 
and the same species is widely diffused in America 
and Europe, though curiously wanting on our 
Pacific coasts, as well as in South America. 
The Sticklebacks and the Szlversides are sea- 
shore fishes, the former of cold, the latter of warm 
regions. Some species of both are now permanent 
residents in fresh water. The Sticklebacks espe- 
cially show all degrees of transition, the strictly 
fluviatile forms being as usual smaller in size and 
weaker in armature than the marine ones. 
The Pirate Perches and the Elassoma are two 
very small families, related to each other, and 
distantly related perhaps to the Sun-fishes. They 
are probably remains of some older fauna, and are 
possibly allied to the Berycozds ; but this relation, 
if real, is not very close. 
The Sun-fishes are peculiarly North American, 
nothing similar being found in any other region. 
Their ancestry is probably to be sought among 
the marine Serranidg, the large-mouthed Black 
Bass? being probably the member of the former 
group nearest the parent stock. 
The fresh-water (striped) Bass® are evidently 
allied to the anadromous members of the same 
group. 
The Perch family is perhaps originally an off- 
shoot from the Sea Bass. It has, however, re- 
ceived a peculiar development in American waters. 
1 Anguilla anguilla Linneus. 
2 Micropterus salmoides Lacépeéde. 
3 Morone chrysops, mississippiensis, etc. 
