THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 127 



and Annelid " is difficult to reconcile with the visible con- 

 trast between the two. Whatever local segmentations there 

 are in an Amphioxus appear to me quite unlike "in prin- 

 ciple " to those which an Annelid exhibits. Could its 

 portion of gut be duly supplied with nutriment, the segment 

 of a low Annelid could carry on its vital functions independ- 

 ently. In the parts of the Amphioxus we see nothing 

 approaching to this. Cut it into transverse sections and no 

 one of them contains anything like the assemblage of struc- 

 tures required for living. The Amphioxus is a physiological 

 whole, and in that respect differs radically from the Annelid, 

 each segment of which is in chief measure a physiological 

 whole. No occurrence of local segmentation in the Am- 

 phioxus can obliterate this fundamental contrast. 



An accompanying contrast tells the same story. On as- 

 cending from the lowest to the highest annulose types we 

 see a progressing integration, morphological and physiologi- 

 cal; so that whereas in a low annelid the successive parts 

 are in large measure independent in their structures and in 

 their lives, in a high arthropod, as a crab, most of the parts 

 have lost their individualities and have become merged in a 

 consolidated organism with a single life. Quite otherwise is 

 it in the vertebrate series. Its lowest member is at the very 

 outset a complete morphological and physiological whole, and 

 the formation of those serial parts which some think analo- 

 gous to the serial parts of an Annelid, begins at a later stage 

 and becomes gradually pronounced. That is to say, the course 

 of transformation is reversed.] 



