292 



NATURAL HISTORY. 



conditions represent alternating generations. The chain Salpas give rise 

 to the solitary forms, and these in turn to the chain generation. This fact 

 was first discovered by the German poet-naturalist, who accompanied 

 Count Romanzoff in his voyage around the world. This was the first 

 known instance of alternation of generations, — a condition which, as we 

 have seen, is very common among the lower invertebrates. 



The lancelet, or Amphioxus, is a small form hardly known outside the 

 museums and laboratories, but there it occupies a foremost place on account 

 of its many interesting anatomical and developmental peculiarities, all of 

 which point to its being a near representative of the group from which the 

 vertebrates have sprung. Its general appearance and size are shown in 



Fig. 289. — Lancelet, or Amphioxus {Amphioxus lanceolatus), natural size. Below, several united 



in a chain. 



our cut, the animal being translucent. It is a vertebrate which lacks ver- 

 tebrae, having only that rod of cartilage which we mentioned just above ; 

 it has no heart, but several of the blood-vessels pulsate ; it has no real 

 brain, the anterior end of the nervous system being smaller than the rest 

 of the spinal cord ; in short, it is a very strange animal, and has at vari- 

 ous times been regarded as a worm and as a mollusc. 



It lives on sandy shores, now darting up and swimming about for a 

 moment, and then settling down to conceal itself in the sand. On our 

 American shores it occurs as far north as Virginia, while other forms are 

 found all over the world. So simple are they, and so great a lack of 

 ordinary characters do they exhibit, that the question is not yet settled 

 whether there be one species or several. One author thinks that there are 

 five species. 



