148 THE HISTORY OF CREATION. 



expressly remark that this sketch, like all similar attempts, 

 l^ossesses only a provisional value. 



The numerous classes distinguished in the tribe of Worms, 

 and which almost every zoologist groups and defines accord- 

 ing to his own personal views, are, in the first place, divided 

 into two essentially different groups or branches, which in 

 my Monograph of the Calcareous Sponges I have termed 

 Acoelomi and Coelomati. For all the lower Worms which 

 are comprised in the class of Flat-worms (Platyhelminthes), 

 (the Gliding-worms, Sucker-worms, Tape-worms), differ very 

 strikingly from other Worms, in the fact that they possess 

 neither blood nor body-cavity (no ccelome) ; they are, there- 

 fore, called Acoelomi. The true cavity, or ccelome, is com- 

 pletely absent in them as in all the Zoophytes ; in this im- 

 portant respect the two groups are directly allied. But all 

 other Wonns (like the four higher tribes of animals) possess 

 a genuiae body-cavity and a vascular system connected with 

 it, which is filled with blood ; hence we class them together 

 as Coelomati. 



The main division of Bloodless Worms (Acoelomi) con- 

 tains, according to our phylogenetic views, besides the still 

 living Flat-worms, the unknown and extinct primary 

 forms of the whole tribe of Worms, which we shall call the 

 PrimEeval Worms (Archelminthes). The type of these 

 Prhnceval Wonns, the ancient Prothelmis, may be directly 

 derived from the Gastrsea (p. 133). Even at present the 

 Gastrula-form — the faitliful historical portrait of the 

 Gastrsea— recurs in the ontogenesis of the most different 

 kinds of worms as a transient larva-form. The ciliated 

 Gliding-worms (Turbellaria), the primary group of the 

 present Planary or Flat-worms (Platyhelminthes), are the 



