148 THE HISTORY OF CREATION. 
expressly remark that this sketch, like all similar attempts 
possesses 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 
Accelomi 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 ecelome) ; they are, there- 
fore, called Accelomi. 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 Worms (like the four higher tribes of animals) possess 
a genuine body-cavity and a vascular system connected with 
it, which is filled with blood ; hence we class them together 
as Colomatt. 
The main division of Bloodless Worms (Accelomi) 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 
Primeval Worms (Archelminthes). The type of these 
Primeval Worms, the ancient Prothelmis, may be directly 
derived from the Gastrea (p. 133). Even at present the 
Gastrula-form — the faithful historical portrait of the 
Gastrzea—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 
