MINUTE ANATOMY OF LIMNOCODIUM. 541 



through the base of another tentacle, not a radial one. The 

 circular canal (c. c.) as seen in cross-section is roughly 

 triangular in shape. The epithelia of the radial canals and 

 the endoderm lamella join the epithelia of the circular canal 

 at the apical angle, while the velum and tentacles arise near 

 the interior and exterior basal angles of the circular canal 

 respectively. On the basal side, i. e. the side between the 

 attachment of the velum and that of the tentacles, the ecto- 

 derm is much thickened and modified to form the " nettle- 

 ring " (net.), and between the nettle-ring and the point of 

 attachment of the velum is the nerve-ring {n. r.). 



Tentacles. — The tentacles are usually carried turned back 

 over the aboral surface of the umbrella, and, like those of 

 many of the Trachymedusse, are aduate to the margin of the 

 umbrella for a short distance. The tentacle roots are not 

 entirely surrounded by mesogloea as are those of Cunina, but 

 only lie in a furrow on the umbrella margin. This attach- 

 ment of the tentacles to the umbrella is doubtless connected 

 with their upright carriage, and is very similar to the condition 

 obtaining in Limnocnida ; but in Limnocodium the embedded 

 part or " root " of the tentacle consists of endoderm only, 

 whereas in Limnocnida the embedded tentacle root is en- 

 sheathed with ectoderm. 



The structure of the tentacles has been described both by 

 Professor AUman and by Professor Lankester. With regard 

 to the question of the presence or absence of an axial cavity 

 and of the condition of the endoderm, the account by Professor 

 Allman (4, p. 133) is as follows : — ''I could find no indication 

 of a cavity in the tentacles; but they do not present the 

 peculiar cylindrical chorda-like endodermal axis formed by a 

 series of large, clear, thick-walled cells which is so character- 

 istic of the solid tentacles in the Trachomedusse and Narco- 

 medusse." 



Professor Ray Lankester, in an addendum to his second 

 paper (3), says, " Endoderm-cells consist of a dense, highly 

 refringent substance, which is somewhat wrinkled by the action 

 of the reagent;" and further, ''In some cases a small amount 



