114 



LOWER VERTEBRATES. 



interopercle, which is very movable. Callichthys has the bony plates on the side 

 arranged in two series, from head to tail, the two meeting about on the level of the 

 eye. The species are said to make nests for their ova, defending them with much 

 spirit, and, at times, to travel overland like the species of Doras. 



The Aegidje are very similar to the Loricariidje, differing mainly in the absence of 

 the coat of mail, and in the presence of maxillary barbels only. There seems to be no 

 doubt of the very close relation of the two famihes. Dr. Giinther observes: "I 

 consider ^r(/es as a naked Xo?7'cana, or, vice versa, Loricaria as a mailed Arjes; 

 and although these forms are sufficiently diversified to admit of further subdivision, it 

 is a most artificial method, by which their natural union is destroyed." The five or 

 six known species of Argldae reach a length of two or three inches only, and inhabit 

 the ponds and springs of the upper Andes on the Peruvian or Pacific slope, where 



Fig. T8.— 17< 



they take the place occupied by the Loricariidie on the Atlantic side. They are 

 locally known as " Preiiadillas." One of the species ( Cydo2num cydopum = Sty- 

 gogenes) has " received some notoriety through Humboldt's accounts, who adopted 

 the popular belief that they live in subterranean waters within the bowels of active 

 volcanoes of the Andes, and are ejected with streams of mud and water during erup- 

 tions. Humboldt himself considers it very strange that they are not cooked and 

 destroyed whilst they are vomited forth from craters or other openings. The 

 explanation of their appearance during volcanic eruptions is that they abound in the 

 numerous lakes and torrents of the Andes, that they are killed by the sulphuretted 

 gases escaping during an eruption, and swept down by the torrents of water issuing 

 from the volcano." {Giinther.) 



In the Claeiid.« the body is eel-like, and the dorsal and anal fins are extremely 

 long, the former extending from the nape to the tail. A peculiar accessory gill is 

 attached to the posterior edge of the second and fourth branchial arches, and is 



