THE ANIMAL KINGDOM 9 



segmentation, in the Appendiculata the muscles and 

 nervous system have become incorporated in the 

 segmentally repeated sacs which give rise to the 

 reproductive organs, and are themselves meta- 

 merically segmented. The nervous system of the 

 Nemertea is also totally different from that of the 

 Appendiculata, being built on the Platyhelminth 

 plan, with lateral dorsal and ventral longitudinal 

 cords, whereas in the Appendiculata there is in- 

 variably the double ventral cord with segmental 

 ganglia upon it. 



The institution and vindication of the Phylum 

 Appendiculata, including a vast quantity of such 

 various organisms as Annelids or segmented worms, 

 Centipedes, Scorpions, Spiders, Mites, Crustacea 

 and Insects, the demonstration that all these widely 

 different organisms can be proved to exhibit an 

 essentially similar plan of organization owing to 

 their having descended from a common ancestor in 

 the remote past, is one of the most noteworthy 

 achievements of zoology in recent times, since it 

 depends entirely on the results of comparative 

 anatomy and embryology, without the assistance of 

 any fossilized remains. The key to the situation was 

 given by the discovery and investigation of a most 

 interesting animal, Peripatus, a true link with the 

 remote past, which helped to bridge over the gulf 

 between the segmented Annelid type and the 



