1898-99. } THE MESENTERIAL FILAMENTS IN ZOANTHUS SOCIATUS. 387 
THE MESENTERIAL FILAMENTS IN ZOANTAUS 
SOCIATUS (ELLIS). 
By J. PLAYFAIR MCMURRICH, M.A.,_ PH.D. 
(Read April 29th, 1899.) 
Several years ago I began a study of the mesenterial filaments of 
Zoanthus soctatus (Ellis), taking this form as a representative of the 
order Zoanthez, and intending, eventually, to extend my observations 
to other species and other groups. Various matters having in the 
meantime presented more pressing claims for attention, I have, so far, 
been unable to carry out my original glan. I have, however, been able 
to study with considerable thoroughness the filaments of the adult 
Zoanthus sociatus, and have also secured some data as to their develop- 
ment in bud-embryos. I have not been successful in obtaining egg- 
embryos of this species, but have observed certain interesting peculiar- 
ities in the development of the filaments in some Zoanthid larve, whose 
parentage could not be determined, some of which I collected myself, 
while others I owe to the kindness of Mr. Alexander Agassiz, who 
obtained them by the surface net in West Indian waters. 
It has seemed to me advisable, notwithstanding the imperfections of 
my materia , to place my observations on record; the more so that it 
seems improbable that I shall be able to carry out my original plan of a 
thorough study of the filaments of the Anthozoa both from the histo- 
logical and the embryological side. 
I.— HISTORICAL. 
Before considering the literature which refers especially to the fila- 
ments of the Zoanthide, a brief review of the literature of the Hexac- 
tinian filaments seems advisable, since it is in this group that the fila- 
ments have been most thoroughly studied. 
Of the structures usually grouped together as parts of a mesenterial 
filament, the acontia, which are extruded from the body by the Sagar- 
tiadz, were naturally the first observed, having been described by 
Dicquemare in 1775, and, according to Contarini, by Gesner as far back 
