174 



ZOOLOGY. 



sure of its tail, or by rubbing against some fixed object, as 

 a shell, it forces the fry, to the number of about a thou- 

 sand, out of its brood-pouch, the young at this time meas- 

 uring about twelve millimetres (5-6 lines) in length. 



Order 8. Plectog nathi. — This group, represented by a 



Fig. 221.— Sun-fish, Mola rotunda, one eighteenth natural size. 



few singular forms, such as the trunk-fish, file-fish, puffers, 

 and sun-fish, is characterized by the union of the bones of 

 the upper and especially the lower jaws. The ventral fins 

 are usually absent, and the skin is often spiny. They are 

 inhabitants of warm waters. The trunk-fish or box-fish, 



