286 



LOWER VERTEBRATES. 



tation, and are wont to twist the very prehensile tail around some stalk, and there 

 remain, with ' neck ' curved upwards, slowly wafting the pectoral fins, and imparting 

 an undulatory or vibratory movement to the dorsal fin. Once in a while a very faint 

 clicking sound may be heard emanating from the fish ; it is like the sound produced by 

 the pincers of an Alpheus shrimp rapidly moved on each other. The eggs are taken 

 care of by the male in a sac open forwards under the tail. 



The Hippocampus heptagonus, or antiquorum, is a common European species; 

 and the Hippocampus liudsonius is a nearly related American form. 



Fio. 100. —Hippocampus heptagonus, sear-horse, and SipJiostoma acus, pipe-fish. 



A remarkable form of this family is the genus Phyllopteryx, of which a couple of 

 species are known from the Australian seas. Both bear cutaneous appendages, and in 

 one of the species (P. eqiies), they are very long and foliaceous, well simulating the 

 vegetation in which it lurks, concealed alike from its enemies and its prey. The eggs 

 are carried by the male, not in a sac, as by the Hippocampi, but imbedded in the soft 

 membrane under the tail portion. 



Order X. — PLECTOGNATHI. 



The next order we have to consider is one exhibiting great variation in external 

 features, and, as a rule, they are quite unlike the typical fishes ; and it is for this 

 reason, rather than because there are any very salient structural features, that the 



