PHYLA OF THE ANIMAL PEDLGREE 5 



5. Enumeration of the Phyla included in the Grades 

 Enteroccela and Ccelomoccela . — The terra "phylum" was 

 introduced by Haeckel to indicate the branches of the animal 

 pedigree of largest size. Setting aside the bifurcation of the 

 ^letazoon stem into Parazoa and Enterozoa, wo use the term for 

 primary branches. The branches into which a phylum divides 

 are called, in accordance with the practice of all systematists since 

 Linnaius introduced the system, "classes"; those into which a class 

 divides " orders " ; those into which an order divides are called 

 families, which are divisible into genera, and these again into 

 species. Breaks may be indicated in any of these groups by the 

 recognition of two or more "grades" within it, whilst divergences 

 of importance giving rise to two or more lines of descent can be 

 further pointed out by the additional groupings furnished by the 

 prefix " sub," such as sub-phylum, sub-class, sub-order, etc. 



AVe recognise the following phyla in the two grades of 

 Enterozoa : — 



Grade A. Enteroccela. 



r Hydromedus/E. 



Phyla -< SCYPHOMEDUS^. Anthozoa. 



\ Ctenophora. 



Grade B. Ccelomoccela. 

 a. Groups which in the present state of knowledge must he regarded 

 as distinct Phyla. 

 Platyhelmia. Nematoidea. Mollusca. 



echinoderma. ciletognatiia. 



Vertebrata Appendiculata Nemertina. 



including the Sub-Phyla including the Sub-Phyla 

 Hemichorda, liotifera, 



Urochorda, Chaitopoda, 



Cephalochorda, Arthropoda. 



Craniata. 



(3. Groups whose relationship to tJie above Phyla is at present obscure, 

 ami are therefore provisionally treated as distinct Phyla. 

 Mesozoa. Acanthocephala. 



Polyzoa. Diplochorda. 



coelia," the distinction which it was intended to indicate by contrast with 

 the terra " Pseudocalia " is no longer defensible. And, inasniucli as the 

 Hertwigs themselves also use the terra " CVulenteraten " in their " Cocloni- 

 theorie " for the lower grade of Enterozoa, it seeras inadmissible that they 

 should apply a word compounded of the same factors (enteron and koilos) 

 to a totally diflerent set of animals. " Enterocoeloniia " and " Pseudo- 

 cceloraia" would more truly have expressed their meaning than the 

 words they emidoyed. The cavity which they discuss in their book is 

 called " the ccelom," not " the ccel." 



