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. Pledognathi. — 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 
inhabitant§ of warm waters. The trunk-fish or box-fish, 
