284 THE HISTORY OF CREATION. 



are the nearest relatives of these exceedingly remarkable 

 Worms, which connect the widely differing classes of Inver- 

 tebrate and Vertebrate animals. That the ancestors of 

 man really existed during the primordial period in the form 

 of these Himatega, is distinctly proved by the exceedingly 

 )"emarkable and important agreement • presented by the 

 ontogeny of the Amphioxiis and the Ascidia. (Compare Plates 

 XII. and XIII., also pp. 152, 200, etc.) From this fact the 

 earlier existence of Sack Worms may be inferred ; they of 

 all known worms were most closely related to our recent 

 Tunicates, especially to the* freely swimming young forms 

 or larvae of the simple Sea-squirts (Ascidia, Phallusia). 

 They originated out of the worms of the seventh stage by 

 the formation of a dorsal nerve-marrow (medulla tube), 

 and by the formation of the spinal rod (chorda dorsalis) 

 which lies below it. It is just the position of this central 

 spinal rod, or axial skeleton, between the dorsal marrow 

 on the dorsal side, and the intestinal canal on the ventral 

 side, which is most characteristic of all Vertebrate animals, 

 including man, but also of the larvse of the Ascidia. The 

 form value of this stage nearly corresponds with that which 

 the larvae of the simple Sea-squirts possess at the time 

 when they show the beginning of the dorsal marrow and 

 spinal rod. (Plate XII. Fig. A 5 : compare the explanation 

 of these figures in the Appendix.) 



