EXPERIMEN'L’AL OBSERVATIONS ON PENNATULTDS. 459 
responsible for the delayed progression. The metabolic 
influence of the contents of the circulating fluids upon the 
tissues bathed by them is not without interest to the physio- 
logist. 
DuriTig fixing operations the contour of the colony and 
especially that of the stalk usuall}^ changed somewhat. 
This was particularly noticeable in the case of Pteroeides, 
in which the fixative re-agent penetrated the thick and tough 
body-walls very slowly, allowing the internal axis to become 
considerably shortened by muscular contractions, and bring- 
ing about a slight invagination of the extreme base of the 
stalk. The normal basal apertures were thus completely 
obliterated, but the slight invagination of the body-wall gave 
the appearance of a single aperture, which is so usual in pre- 
served specimens of Pennatulids that it has been frequently 
described as a month opening by early writers (fig. 3b), 
(Linnajus, Della Chiaje, etc.), and as frequently denied by later 
ones (Marshall, Pennatnla; Hubrecht, Echiuoptilum). 
In the case of Pennatnla it was possible to fix and pre- 
serve specimens in which the two apertures of the dorsal and 
ventral canals were discernible, but in Pteroeides and other 
forms all the basal and dorsal pores were obliterated during 
the operations of fixing and preserving. 
The peristaltic dilatations and contractions described by 
Bohadsch and Kblliker were observed in the case of Pteroe- 
ides and Penjiatula, but in all cases the movements were 
confined to the stalk and rachis, and were somewhat lethargic 
even in freshly captured and apparently healthy specimens, 
in some instances being so slight as to be barely perceptible. 
3’here can be no doubt that specimens examined in captivity 
suffer considerably in this respect from their change of 
environment, but a study of the internal anatomy of the stalk 
aTid rachis of Pteroeides, Anthoptilum, Virgularia, and 
Pennatnla furnishes indisputable evidence at least of the 
Tnuscular activity of the axis as a boring organ, and suggests 
also the probability of its function as a propelling organ in 
these genera. 
VOL. 54, PART 3. NICW SERIES. 
33 
