AND THE LOWER ANIMALS. 93 



Until the year 1856 it was thought by all naturalists 

 that batrachia were the only vertebrate beings which 

 underwent metamorphoses. It was M. Auguste 

 Miiller who first proved that phenomena exceedingly 

 like those we have described may also take place in 

 fishes. This naturalist has proved beyond all doubt 

 that the Ammocetidse are nothing less than the larvae 

 of the lampreys. However, in reaching their perfect 

 state, they have a much shorter distance to travel than 

 the tadpoles. In their case, both larva and adult 

 breathe by branchial organs; the ammocetis is in 

 reality as much a fish as the lamprey. The only 

 apparatus which undergo a decided modification are, 

 the mouth, which is converted into a sucking and 

 chewing organ, the anterior portions of the digestive 

 tube, which are connected with the orifice of the 

 mouth, and the series of bones and muscles associated 

 with the respiratory function.* If these changes 

 took place in the egg, instead of in the animal leading 

 an independent existence, we should simply term 

 them transformations ; but as they are accomplished 

 after the animal has left the egg, they belong to that 

 series of phenomena collectively styled metamor- 

 phoses. 



* "Ueber die Entwickelung der ISTeunaugen." — Miiller's Archives, 

 1856. The ammocetis had been considered almost the lowest form 

 of fish, until this great discovery of M. Auguste Miiller. The 

 amphioxus, which is a still more aberrant fish, and which approaches 

 in some respects certain armelides (Dorsibranchiata), was, and is 

 still, regarded as the lowest member of the class Pisces. But we 

 are now justified in asking whether such an exceptional creature as 

 the amphioxus is a perfect animal. There are many features in its 

 organization which remind one of the common river ammocetes. 

 May it not be the larva of Petromyzon marinns, or of some other 

 species ? 



