EXPERIMENTAL OBSERVATIONS ON PENNATULIDS. 445 
Bohadscli and Ellis of the existence of a mouth or of any 
basal opening to the exterior that the statement ‘'os baseos 
commune rotundum” was omitted in the diagnosis of the 
genus in the eleventh and subsequent editions of Linnmus’ 
‘ Systema Xatnrte.’ 
Later, when the knowledge of the colonial habit of the 
“sea pens” had become established ‘Ellis and Solander’ 
(1786), in a joint publication, made the following state- 
ment : 
“ They have no opening at the bottom as was formerly 
thought, nor any other passage but through their polyp 
mouths”; but notwithstanding this emphatic denial 0. F. 
^Miiller (1788) recorded the presence of a pore at the base of 
the stalk in Kophobelemnon, and later Della Chiaje (1827) 
described, with accompanying illustrations, the interesting 
occurrence of a basal pore in specimens of Pteroeides 
spinosnm, Pteroeides griseum and Pennatula rubra, 
and furthermore stated that the pore communicates with the 
canals in the stalk. 
These observations were confirmed by Kolliker (1872), 
Avho noticed in some cases a single pore, and in others two 
pores at the base of the stalk in Pteroeides and Penua- 
tula. In 1875 Kolliker’s statement was further confirmed by 
Schultze, but Hubrecht (1882, p. 572) was unable to observe 
any basal aperture in the case of the new genus Echino- 
ptilum,and Marshall (1887, p. 29), who appears to have made 
the most recent observation on the subject, remarked that 
he was unable to confirm KollikeFs statement with regard to 
the presence in Pennatula of a minute orifice at the base of 
the stalk opening into the canals. 
I have therefore sought experimental evidence, which is 
recorded in the present paper (pp. 452-459), in the hope of 
obtaining a satisfactory and final solution of this questionable 
point. 
The early accounts of the active swimming movements of 
Pennutalids have been, during recent yeai's, somewhat dis- 
credited. There can, however, be little doubt that they 
