ON THE ANATOMY OF THE FAMILY OF THE MEDUS/E 1/ 



an upper dilated sac, by which it communicates with the circular canal, 

 fig. 8. 



The marginal tentacles of Oceania resemble these in all points ; 

 they are double-walled, communicate freely with the circular canal, 



.and contain an immense number of minute thread-cells in their outer 

 wall, fig. 15. 



35. In Phacellophora there is no distinct marginal circular canal, but 

 the sixteen radiating canals are very wide and sacciform, and com- 

 municate only by anastomosing marginal branches. Eight of the 

 canals are narrower and run to the marginal corpuscles. The alternate 

 ■eight are very much wider, and their outer, under surface is beset with 

 a curved series of long tentacles, fig. 18. Now the lower wall of the 

 canals is composed of the two " foundation membranes," and the 

 tentacles are simply prolongations of these membranes ; they are 

 therefore double-walled, and contain a cavity continuous with that of 

 the canal. At their upper part they are thicker than below, where 

 their outer membrane is developed into spherical processes containing 

 multitudes of thread-cells and closely resembling those on the genera- 

 tive membrane (30).' The inner cavity becomes obliterated at the 

 lower part of the tentacle, fig. 19. 



36. The large interbrachial tentacles of Cephea are processes of the 

 branched arms. For the greater part of their length they have the 

 same structure as the arms, i.e. consist of a dense, thick, transparent 

 •outer substance and an inner membranous wall inclosing a tubular 

 canal ; but at the extremity they are thickened, and the outer wall is 

 raised into a number of small pyriform processes, x-g-u-th of an inch in 

 •diameter, thickly covered with minute spherical thread-cells, -s^Vxrth of 

 an inch in diameter. At the same time the central canal becomes 

 branched out into a kind of plexus, which occupies the interior of the 

 enlarged end of the tentacle, fig. 37. These tentacles are two inches 

 or more in length and xVh of an inch in thickness, but other smaller 

 tentacles, fths of an inch in length by -nVth of an inch in diameter, 

 depended from the arched concavity of the brachiferous plate. Their 

 general structure much resembled that of the foregoing, except that 

 the central canal terminated in a blind simple extremity, and that the 

 pyriform bodies extended rather further up the stem. 



Beside these there was a third small kind of tentacles, which 

 appeared as small blue points among the stomachs. These were 

 clavate bodies placed without any regular order in the axils between 

 the stomachs, and containing an internal cavity which communicated 

 with the nearest branch of the common canal. A series of pyriform 

 processes, exactly resembling in form those above described, was 

 VOL. I C 



