56 



Above this point the ancestral Polychseta must have 

 acquired parapodia, the characteristic lateral appendages of 

 the Annelides, upon which the bundles of setae are borne. 

 Various processes more or less of a sensory nature were also 

 developed from the anterior end of the body (the prae-oral 

 lobe), making it more of a specialised head. From this 

 ancestor or some very similar form must be derived the 

 curious little group of Myzostomida* which are found as 

 ecto-parasites on the Crinoidea. They are certainly degene- 

 rate, and have been much modified since they left the main 

 stem. 



The series of ancestral Vermes finally terminates by 

 breaking up into the progenitors of the numerous closely- 

 allied groups of Polychseta now existing. These are therefore 

 the highest members of the large and very heterogeneous 

 phylum Vermes. Unlike the Oligochaeta they are nearly all 

 dioecious and marine forms, and have no highly specialised 

 reproductive organs. In some of the groups (Tubicolous 

 forms) a considerable amount of heteronomy is exhibited. 



There remains now only the great and important phylum 

 Chordata, which contains the whole series of vertebrate 

 animals. The ancestral Chordata as we have already seen 

 arose from the main axis of the Vermes rather low down. 

 Hubrecht t maintains that there is a closer relationship 

 between the Chordata and the Nemertida than my table 

 shows ; he regards the sheath of the protractile proboscis of the 

 Nemertean as being the origin of the notochord, and considers 

 that the Proto-Chordata arose from the Nemertida. Semper! 



* Beard, Mitthl. Zool. Stat. Neapel., Bd. v., p. 544 (1884) ; and also 

 L. von Graff, Challenger Zoological Reports; " The Myzostomida," vol. x, 

 part xxvii (1884). From the adult anatomy Graff considers the Myzosto- 

 mida as being allied to the Tardigrada. 



■\ Quart. Journ. Micros. Sc, vol. xxiii, no. xci, p. 349, July, 1883. 



+ Arbeit, a.d., Zool.-Zoot. Instit., Wiirzburg, vols, ii and iii (1875-77). 



