1888 - 89 .] Mr G. Brook on Homologies of the Mesenteries. 37 
development of the mesenteries in all these forms has led me to 
believe that their arrangement cannot be explained in accordance 
with the current views on the subject. With the exception of two 
pairs of directives, the mesenteries do not appear to show the paired 
arrangement usually looked for. The mouth is usually elongated, 
and is supported at each end by a pair of directives. The muscula- 
ture is, however, very imperfectly developed, and I have not yet 
made out the position of the retractor muscles. In Gladopathes , 
n. gen., there are only six mesenteries present. Two pairs of direc- 
tives occupy the extremities of the stomodseum, as in other types, 
and two other mesenteries are situated in the transverse axis — that 
is to say, at right angles to the long axis of the stomodseum. These 
bear the reproductive organs. These six mesenteries I have termed 
“ primary;” all are of considerable length; those in the transverse 
axis are, however, somewhat longer than the others. In Antipathes , 
&c., there are ten mesenteries — six primary ones as in Cladopathes , 
and four short “secondary” mesenteries, one on each side of the 
transverse mesenteries. In Leiopathes there are twelve mesenteries, 
six primary and six secondary. In horizontal sections passing just 
beneath the mouth, the transverse axis is seen to be occupied by an 
interseptal space, and not by a mesentery. On each side of the 
stomodseum there are six mesenteries, three on each side of the 
interseptal space occupying the transverse axis. A little lower 
down, however, it is seen that two mesenteries bordering the trans- 
verse axis, one on each side of the stomodseum, become lost, and as 
they do so the other two become more important and approach the 
middle of the stomodseum so as to occupy the transverse axis. The 
arrangement is then as in Antipathes. 
It appears to me that this arrangement receives its explanation by 
a comparison with the order in which the first twelve mesenteries 
are developed in Hexactinise according to LacazeDuthiers. In Actinia 
and Heliactis the first twelve mesenteries are developed in pairs 
which are not adjoining mesenteries, but are situated one on each 
side of the stomodseum. The order in which they are developed in 
Heliactis bellis (and in Actinia equina ?) precisely corresponds with 
their relative length in Leiopathes. The first pair to be developed 
are those corresponding to the transverse mesenteries in Anti- 
pathidse ; next follow the two pairs of directives, and afterwards 
