72 THE VOYAGE OF H.M.S. CHALLENGER. 



Whilst the large coronal muscle with its circular fibres contracts the distal part of 

 the suburnbrella, the muscle of the swimming bell (" musculus codonoides ") with its 

 longitudinal fibres answers for the proximal half of the suburnbrella. The most import- 

 ant longitudinal muscles of this system are the eight strong deltoid muscles ("musculi 

 deltoides," md ; PI. XIX. fig. 6 ; PL XX. fig. 8). They are very powerful, ecmflaterally 

 triangular, and touch the proximal margin of the coronal muscle with their broad bases, 

 whilst their truncated point is directed upwards and their longitudinal fibres consequently 

 diverge centripetally. The four weaker perradial deltoid muscles (md') are inserted by 

 their truncated point at the distal end of the gastral openings, in the subumbral wall of 

 the four cartilaginous palatine nodes (gh). The four stronger interradial deltoid muscles 

 {md"), on the other hand, are longer, and inserted further up on the subumbral wall of the 

 four septal nodes (hi) in the middle of the length of each pair of genitalia between the two 

 halves. Between these, the deltoid muscle also forms, above the septal node, a thin band- 

 shaped prolongation, which runs centripetally as far as the pylorus ("musculus intergenitalis," 

 fig. 8, ms). Besides these, a stronger longitudinal muscle, which I wdl call "musculus 

 congenitalis" (fig. 8, mn), runs into the suburnbrella on the two lateral margins of each of 

 the four gastral openings, between them and the limiting genital bands. It springs with 

 a broader base from the inverted lateral margin of the perradial deltoid muscle, runs, 

 gradually becoming narrower, up above between the gastral ostium and the limbs of the 

 genitalia, and is inserted above with its narrow end in the pyloric ring (fig. 8, gy). 

 Finally, a narrower and very much weaker longitudinal muscle, which may be termed 

 " musculus axogenitalis," runs in the middle of the eight genitalia, and, in fact, on the 

 midrib between the two limbs of each genitalium (fig. 38, mx). On the whole, therefore, the 

 system of the muscle of the swimming bell (" musculus codonoides ") is divided into four 

 stronger interradial and four weaker perradial area? ; the four interradial deltoid muscles, 

 the four intergenital muscles and the eight axogenital muscles belong to the former ; the 

 four perradial deltoid muscles, and the eight congenital muscles to the latter. 



Although the circular system of the distal coronal muscle, and the longitudinal system 

 of the proximal swimming bell muscle, form by far the most important part of the 

 subumbral muscidar system, it is represented by weaker muscles in other parts of the 

 suburnbrella. The circular fibres already mentioned, in the wall of the basal funnel 

 cavities, belong to it on the one hand, and the longitudinal fibres on the concave axial side 

 of the marginal lobes, which we shall briefly term " lobe muscles " (" musculi lobares," mh), 

 on the other. Each of the sixteen marginal lobes has in its thin subumbral wall a pair of 

 such longitudinal muscular bands, which run to both sides of the medial (subraclial) lobe 

 clasps (Ik), and clearly correspond to the well-known stronger lobe muscles of the Disco- 

 medusse. 



The gastro-vascular system of Periphylla mirabilis (PL XX. figs. 8-11; PL XXI. 

 figs. 12-20 ; PL XXII. fig. 22 ; PL XXIII. figs. 29-31) is distinguished from that of all 



