256 



LOWER VERTEBRATES. 



hundred being more or less satisfactorily known. Most of them have a stout body- 

 diminishing from the head to the tail, but some become quite elongated, and a few 

 are compressed and oval ; the scales in most have a pectinated hinder margin which 

 is angulated at the middle, whence the striae diverge forwards, but some of the scales 

 are cycloid, and a number have only cycloid scales ; few are entirely naked ; there 

 never is a lateral line ; the head is generally short with bulging cheeks ; the branchial 



Fig. 145. — Periophthalmus koelreuta-i. 



apertures are more or less restricted to the sides ; generally, there are two dorsal fins, 

 and in most the first has six spines, of which the last is separated by a wider interval 

 than are the others ; in some, however, the spines are more numerous, and in others, 

 the fin is continuows with the second ; the ventrals are thoracic, and mostly have a 

 spine and five rays, the inner of which are largest ; in most there is also a connecting 

 membrane in front between the sjjine, and behind between the innermost rays, 

 resulting in- a funnel-shaped sucker. Finally, a papilla is developed next the anus. 



