530 
COELENTEKATA. 
a metamorphosis, the young ones being without lobules, but provided with 
tentacles, which are lost before attaining the adult state, &c. In the con- 
cluding chapter, Agassiz attacks Hackel’s “ Gastrcsa theory ” [vide infrd^ 
p. 633], urging, that the walls of the primitive gastric cavity are in 
Actiniae^ worms, and Hydroids formed by the endoderm, in Echinoderms, 
Ctenophora, aud some Diacophora by the ectoderm ; the “ Gastrulai ” of 
these two types therefore cannot be regarded as homologous. In advocat- 
ing the homologies between Ctenophora and larval Echinoderms, Agassiz 
agrees in the main with Metschnikoff, though differing in some particulars. 
Ctenophora should be placed with Echinoderms in one great division, or 
i\iQ Acalephoe divided in Medusidce (D iscojihor a amdi Hydroida) and Cteno- 
phora, these being, on account of their embryology, more closely allied 
to Echinoderms than the other Acalephce. Agassiz's criticism of 
H tick el’s theory is translated in Arch. Z. expdr. iv. pp. ix.-xiii. 
