SURFACE-SWIMMING FAUNA (VERTEBRATES). 123 



Many of these are characterised by remarkably 

 long fin rays, by their large eyes, or by other 

 features which may be regarded as special modi- 

 fications for their peculiar habits. 



A very interesting genus is Scopelus, which is 

 found very widely distributed in tropical and 

 other seas. Some of the species live in very deep 

 water, and are purely abysmal in habit, but most 

 of them rise to the surface at night, when they 

 may be caught in immense numbers. In form 

 they are not unlike a small Sprat, but they 

 exhibit on each side of the body a series of 

 minute eye-like organs, which emit a phosphor- 

 escent light. 



In addition to these Fish which are found far 

 out in the open ocean, there are several genera, 

 which form an important feature of the surface 

 waters in the neighbourhood of the coasts. 

 Among them we find such valuable food-fish as 

 the Herrings, Sprats, Mackerels, and Pilchards. 



The complete history of the Herring has yet 

 to be written, for, notwithstanding the laborious 

 investigations of several naturalists, working 

 independently, or as officers of the Marine 

 Biological Association and similar Institutions, 

 there are some facts and stages which have, up 

 to the present time, escaped observation. 



The Herring species is divided into a number 

 of races, which, differing from one another only 

 slightly in anatomical characters, have different 

 seasons for depositing their eggs. This fact 

 has only recently been thoroughly established ; 

 and while it assists us greatly in the task of 

 completing the history of the Fish, it definitely 



