REPORT ON THE DEEP-SEA MEDUSJ3. lxi 



velarium ; it is most strongly developed in the Cubomedusse (PI. XXVI. , mv). Comp. 



§§ 66-70. 



§ 89. Eadial muscles of the subumbrella (" myosystema radiale "). Whilst the cir- 

 cular muscular system of the Medusae is almost invariable composed of transversely stri- 

 ated fibres, the radial muscular system in both sections of this class, is formed for the most 

 part of smooth, not transversely striated, muscular fibres ; these run in vertical meridian 

 planes, sometimes more radially, sometimes more longitudinally, parallel to the principal 

 axis. The radial muscular fibres are also divided into three sections analogous to those 

 of the circular muscular fibres ; the proximal longitudinal muscles of the oesophagus and 

 of the oral organs, and also of the gastral peduncle ("musculi proboscidales"), the middle 

 bell muscle ("musculus codonoides"), and the distal longitudinal muscles of the umbrella 

 margin ("musculi marginales"). The system of the proboscidal muscles ("musculi 

 proboscidales ") forms the proximal part of the radial system ; we may include in it, the 

 true longitudinal muscles of the oesophagus and of the different oral organs (oral lobes, 

 oral arms), and also the longitudinal muscles of the gelatinous gastral peduncle (e.g., in 

 the Octorchidae System, taf. xii., xiii. ; Geryonidae, System, taf. xviii.) ; in proportion as 

 the gastral peduncle is developed as a movable " proboscis," the four, six, or eight broad 

 longitudinal bands of muscles, which run in its upper surface between the ascending 

 radial canals, become more powerful. Of the longitudinal muscles of the oesophagus itself 

 the four perradial are usually most strongly developed. They run on the four folded 

 oral lobes or the large oral arms which have originated from them, on the abaxial side of 

 their midrib, and radiate, often in bunches, towards their frilled oral margin. In most 

 Medusae the second and middle section of the radial muscular system, whose separate 

 part we include under the name of bell muscles, is far more important. All the longitu- 

 dinal muscles of the subumbrella which lie between the base of the " proboscis " and the 

 umbrella margin belong to it. The bell muscle (like the coronal) not unfrequently (namely, 

 in a part of the Narcomedusae and Stauromedusae) represents a single, bell-shaped, 

 arched muscular plate, consisting of diverging radial fibres ; it is usually divided into a 

 number (four, eight, sixteen, or more) of separate longitudinal muscles. In most 

 Craspedotae four or eight such longitudinal muscles run on the subumbral surface of the 

 radial canals, but often also four or eight in the middle between these. We conse- 

 tpiently find usually four perradial longitudinal bands (w#>) and four interradial (mi) 

 between them, beside often eight adradial, rarely more. They are sometimes simple, 

 unpaired bands, which run exactly in the middle line of the radial canals (e.g., Pectyllidae, 

 Pis. III.— VIII.), sometimes paired bands, enclosing the two lateral margins of the 

 canals (e.g., Tiaridae, System, taf. iv. figs. 2, 3). The subumbral radial muscles are most 

 strongly developed in those Craspedotae which form circumoral buttresses (mesenteries or 

 mcsogonia). Many Tiaridae have four such perradial mesenteries, whilst the Pectyllidae 

 have eight principal mesenteries (PL IV. fig. 3, PI. VIII. fig. 9, wr). They lie as four or 



