66 NILS HJ. ODHNER, MOLLUSCA. 
Near the pore of the cnidophorous sac, this latter is filled with secretion, in 
which appear many cnidocysts (nem.); these are very small, being only about 3—5 u., 
and ovoid in shape. 
In the morphology of the cnidophorous apparatus, Madrella represents a primi- 
tive stage in comparison with other Eolids, not only in the position of the sacs on 
the notaeum at the base of the papillae, but also in their structure, which is not so 
specialized as in Aeolididae. The collar is very short, with a transgredient epithelium 
which is not ciliated (as in Aeolis papillosa e. g.). The muscular layer of the cnido- 
phorous sac shows a primitive stage inasmuch as it is not yet differentiated 
into a longitudinal and a circular stratum (as in Ae. papillosa) and as it very 
clearly passes into the fibrillar covering of the hepatic coeca, thus showing its origin 
from the connective tissue. Madrella, as a consequence, shows the way of develop- 
ment of the cnidophorous sacs of the Åeolididae. 
Fig. 19. Jaws of Madrella ferruginosa A. & H., Fig. 20. Radula of Madrella ferruginosa A. & H. 
from above. 
The papillae of the notaeum (fig. 17) are simple prolongations out of the con- 
nective tissue that fills their interior; they have no hepatic diverticula, but are furn- 
ished with a cnidophorous sac within their root. Their apices are expanded like a 
pins head, as shown in the figure. 
Interior anatomy. Concerning, first, the alimentary canal, we find that the 
bulbus pharyngeus is of considerable size. 
The jaws (fig. 19) are two chitinous lateral plates of a yellowish horn colour, 
combined in front on their upper side by a bridge of a cartilagineous consistency 
and of white colour. This unpaired section has a thicker anterior margin, with some 
rifle-like stripes of a firmer consistency, but not forming prominences on the surface. 
Its hinder part is lameiliform and tapers towards its posterior margin. 
The lateral parts of the jaws have an elongated wing-form. Their foremost 
lower ends, at the sides of the connecting bridge, are swollen and rounded and with 
no trace of denticulation. They each bear on their under part a small projection 
of the same swollen habitus, representing a rudimentary masticatory process. The 
dilated posterior parts of the jaws are furnished, on the outer as well as on the 
inner walls, with crests running one in a longitudinal, the other in a transversal 
