700 



MEDUS.E OF THE WORLD. 



The canal-system of the mouth-arms is as follows: 4 vessels arise from the perradial angles 

 of the lower side of the central stomach and extend downward into the arm-disk in the 4 

 perradii. These 4 primary canals bifurcate and the 8 branches extend down the 8 mouth- 

 arms. The 16 lateral vessels which go into the scapulets arise from these 8 mouth-arm canals. 

 The central mouth is always present in very young medusx but it usually disappears 

 in the adult. When this mouth is present, or more or less vestigial, we often find a correspond- 

 ing complexity in the mouth-arm canals, for in this case the 4 perradial canals from the corners 

 of the lower part of the central stomach extend downward beyond the points of origin of the 



FIG. 422. Rhizostoma pulmo. From life, by the author, at Naples Zoological Station, December, 1907. 



I, oral view of bell with mouth-arm removed. One half of the surface shows sector of circular muscles, and 

 the other half shows the muscles removed to reveal the canal-system, n, side view of mouth-arms 

 with sections of same, in, section of arm-disk immediately below scapulets. iv, oral view of arm- 

 disk showing persistent central mouth opening, v, sense-organ from exumbrella side. 



8 mouth-arm canals; upon reaching the cruciform, central mouth, each of these 4 canals 

 forks and the 8 branches extend outward along the 8 lines of the frilled mouths, becoming 

 confluent with the 8 main, mouth-arm canals in the j-winged parts of the mouth-arms. A 

 detailed description of the canal-system is given by A. Brandt, 1870. 



The gelatinous substance of the disk is creamy-yellow to milky, or rusty-yellowish and 

 translucent. Marginal lappets dark cobalt or violet to blue. The sensory-clubs are tipped 

 with orange, which colors the concretions. The frilled mouths are dull orange, yellow, or 

 brownish-yellow, and the outer parts of the terminal knobs are tinged with the same color. 

 Gonads yellowish, all other parts translucent. 



