EXPERIMENTAL OBSERVATIONS ON PENNATULIDS. 451 
Virgularia the radial canals described by Marshall have 
communications with the exterior as in Scytaliopsis. 
These supplementary canals, according to Marshall, do not 
occur in Pen na tula or Funiculina. 
The occurrence of the “radial canals” in Virgularia 
is no doubt correlated with the paucity of the zooids. This 
modification has probably been brought about by the insuffi- 
ciency of the zooids, to serve hydrostatic and possibly also 
nutritive purposes. 
Nematocysts, 
As a general rule the Pennatulids are less formidably armed 
with those weapons of offence and defence — the thread-cells 
or nematocysts — than the Alcyonidae. 
The tentacles are usually smooth and filamentous, and lack 
the characteristic warted appearance of those of Alcyonids, 
in which each wart is a battery of poisoning and paralysing 
thread-cells. Nematocysts of the usual type are present, but 
in considerably smaller numbers, and are more or less uni- 
formly distributed in the general ectoderm of the tentacles. 
From their constitution and habits Pennatulids would appear 
to be less voracious in their habits than are Alcyonids gene- 
rally, and are apparently more dependent upon the supply of 
nutriment suspended in the sea-water in the form of organic 
particles, which may be carried into the zooids and canals by 
inflowing curi’ents, where they are ingested and digested by 
the mesenterial filaments of the autozooids, as in Alcyonium 
(Pratt), or by any epithelial surface of the canal system 
(fig. 9). 
The FiXPERIMENTS. 
The experiments recorded in the present paper were 
performed in the Zoological Laboratories of the Marine 
Biological Station at Naples during the month of April, 
1905. 
