LlMNOCODIUM (CRASPEDACUSTES) SOWERS II. 359 
than does the single row of thickened cells which is found in the 
larger and typical Trachyline Medusie. 
The woodcut (fig. 2) represents the Medusa in an attitude 
which it not unfrequently assumes when at the bottom of the 
vessel in which it is confined. When this retroversion of the 
disc is effected^ the velum may take the position of a band ex- 
ternal to the margin of the retroverted disc, or may also be 
retroverted, as in the figure. In this case the tentacles are all 
more or less concealed in the concavity of the retroverted disc, 
and accordingly I have not represented them in the figure at all. 
When in this position the Medusa supports itself on the manu- 
brium as a stalk, exerting a feeble adhesive action by means of 
the quadrifid lobes of the oral aperture. 
This figure also serves to show the position and form of the 
gonads {Go) on the radiating canals, which are omitted in 
figure 1. 
Fig. 3. — Diagram of margin of the disc to show tentacles and marginal 
ring. MRy marginal ring ; Tx, tentacle-axis ; Try tentacle-root. 
Insertion of the tentacles , — The tentacles do not arise from 
the edge of the disc, but in three more or less distinct tiers, 
indicating a relative centripetal movement of the tentacles 
during the growth of the disc, as in many Trachyline Medusas. 
The four perradial tentacles are furthest from the marginal 
ring and their free portion rises from the jelly-like convex surface 
of the disc at some distance from the margin. At the same time 
the cartilaginoid axis of the tentacles is continued beneath the 
ectodermal tissues centrifugally towards the cartilaginoid sub- 
stance of the marginal ring. It is this structural arrangement 
which favours the peculiar vertical carriage of the tentacles, 
since if they are to be directed downwards tow’ards the mouth 
VOL. XX. — NEW SER. A A 
