53 



a tree or a leaf could not be produced in the same way and yet 

 retain their original character. They can however be repeated 

 and indeed we find in organisms in which growth in length occurs 

 in this way that lateral organs are repeated, and not drawn out 

 and this fact may be at the bottom of metameric segmentation. 

 If so it follows that metameric segmentation may have arisen 

 independently in many different phyla and that it is a result of 

 growth in length from a definite growing point ; and as the growing 

 points may have had different origins, there need be no homology 

 between the metamerism of one phylum, for instance the Annelida, 

 with that of another phylum, for instance the Vertebrata. 



Fig. 30. Dolichoglossus serpentinus. 

 df dorsal furrow of proboscis ; br gill clefts ; g gonads ; v bright vermilion spots. 



As regards Balanoglossus it seems probable that there is no 

 deuterogenesis, or if it occurs it soon dies out altogether. The 

 great increase in length of the trunk is due to general interstitial 

 growth. This seems probable from the fact that the bright spots 

 which occur on the trunk of Dolichoglossus become gradually 

 more and more separated from one another as the organism 

 elongates, Fig. 30. 



The bright vermilion spots are the remnants of pigment formed 

 in the gonads, and probably of the nature of excretory products. 

 The gonads, however, are closely packed against one another, 

 whereas the spots towards the end of the trunk are perhaps an 



