MORPHOLOGY. 
GENERAL STRUCTURE. 
In that work of genius the “ Kalkschwamme ” of Haeckel the Calcareous sponges 
(Megamastictora) are traced both ontogenetically and phylogenetically to a primitive 
Ascon-like ancestor (Olynthus). In the non-calcareous Sponges {Micromastictora) the 
researches of embryologists ^ have made us acquainted with a primitive ontogenetic 
form which may be distinguished as a Rhagon,^ but this, unlike the Ascon, is only known 
in a transitory larval stage, and is not represented by any persistent adult form. 
0 . 
Fig. I. — Diagrammatic vertical median section through a Rhagon. S., spongophare ; H., hypophare ; 0., oscule ; G., paragastric 
cavity ; fl., flagellated chamber ; a., apopyle ; p., prosopyle ; e/c., ectoderm ; ev., endoderm ; fi., mesoderm. 
It has the form of a more or less hemispherical sac, the upper part {spongophare 
rising dome-like from a flat attached base {hypophare ) ; its walls consist of 
1 Keller, Eeniera fertilis, Zeitschr. f. wiss. Zool., Bel. xxxiii. pp. 317-349, pi. xix. fig. 23, pi. xx. fig. 24 ; Schulze, 
Placina monolopha, op. cit., Bd. xxxiv. pp. 416-423, pi. xxii. fig. 28 ; Heider, Oscarella lohularis, Ari. Zool. Inst. Wien, 
Bd. vi. pp. 1-62, pi. ii. figs. 18-20. 
2 pi'i, pAyog, it, a grape. 
^ (feepeg, eog, rc, a cloth, sheet, web. 
