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 
remarkable and important agreement presented by the 
ontogeny of the Amphioxus and the Ascidia. (Compare Plates 
XII. and XIITL., 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 larve 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 larve of the Ascidia. The 
form value of this stage nearly corresponds with that which 
the larvee 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.) 
