COLLOMIC SACS 



of important differentiations and consequent development of new 

 organs, such as genital ducts and renal excretory glands, besides 

 aH'ecting the mechanical conditions of the body-wall and muscles, 

 and the diffusion of chemical products within the body. 



A me 



FIG. 3. TRANSVERSE SECTIONS OF 

 Two STAGES OK THE LARVA OF 



THE liRACHIOPOD ARG1OPE TO 



SHOW THE ORIGIN OF THE COELOM 

 AS A PAIR OF ENTEROC<KLOUS 

 POUCHES. 



.4, younger stage. 1>1, blastopore ; 

 pv, right Cd-loinic pouch continuous 

 with ?(i*', the archenteron. Ji, later 

 stage, the cu.-loniic' pouch 0>r) is now 

 shut on" from the archenteron, i/ie ; 



/'' I^TWU^V/T ''' t(>1 "l' oriir y bristles. (After Ko\va- 



lewsky, from Balfour.) 



Accordingly we divide the Enterozoa into those in which the 

 sole cavity is the enteron the Enterocoela and those in which 

 the coelom is present as an independent second cavity the Calo- 

 moooela. 1 



Grade B. CCELOMOCCELA. 



Grade A. ENTEKOCCELA. 



I 



ENTEROZOA. 



1 The two grades which I here call Enteroca-la and (.Velomocu-la are 

 often designated Coclentera and Coelomata. The word Ccclenterata (due 

 to Leuckart, 1848) has been used by some authors. It seems to me that 

 it is legitimate to transpose the components of Ca-lentera so as to form 

 the word Enterocoela, and we then are able to form a very much better 

 pair to it than is Ca'lomata (Haeckel's term), by coining the word 

 (Vlomocoela. The contrast of animals whose sole cavity is the enteron 

 or gut-chamber with those which have a coelom as an essential and dis- 

 tinct cavity is thus clearly expressed. 



The use of the term enteroca'l for the coelom itself, and of the word 

 Enteroccclia for a large division of cojlomocu-lous animals by the 

 Hertwigs may seem to render the conversion of Ccelentera into Entero- 

 ccela inconvenient. But the word " enterocoelous " or " enteroco?lic " is 

 still quite appropriate as a description of the early phase of development 

 of the ccclom for the very same reason which justifies us in calling 

 polyps and medusae, Enterocoela or Ccelentera, viz. that we refer to the 

 existence of a cavity which is in origin in the one case, and permanently 

 in the other a part of the enteron. As to the Hertwigs term " Entero- 



