142 NATURE STUDIES 



PART V. LINKS BETWEEN BACK-BONED AND 

 BONELESS ANIMALS. 



IN the present paper I purpose to give a,n outline of 

 the means whereby the zoologist has been enabled to 

 supply " links " between the Vertebrate, or " back- 

 boned " animals, and the Invertebrate, or " boneless " 

 animals. Ever since the time of Lamarck, the dis- 

 tinction between the highest, or Vertebrated animals 

 (fishes, frogs, reptiles, birds, and mammals or quad- 

 rupeds) and the Invertebrate groups, has been recog- 

 nised as one of very clear nature. And modern 

 zoology, dealing merely with the structure of the 

 animals in question, fully recognises the apparent gap 

 which intervenes between the great array of boneless 

 animals such as worms, insects, shell-fish, &c. and 

 the "backboned" group. But, as in many other 

 cases, a closer examination of the lowest Vertebrate 

 group seems to demonstrate that the gulf between 

 the highest animals and their Invertebrate neighbours 

 is by no means so wide or impassable as, at first 

 sight, it appears to be. The lowest fish and Verte- 

 brate is the Amphioxus, or Lancelot (Fig. 10). This is 

 a little clear-bodied fish formerly regarded as a kind 

 of slug found inhabiting sand-banks in various 

 quarters of the world. It attains a length of an inch 

 or two, and is pointed at each end. It has a kind of 



