80 Proceedings of Royal Society of Edinburgh. [sess. 
zooid is placed. Only one pair of mesenteries ever bear reproduc- 
tive organs ; these occupy the transverse axis, and are situated one 
on each side of the stomodseum. The transverse pair of mesenteries, 
on account of their position, have a greater horizontal breadth than 
any of the others, and they are also usually somewhat longer than 
those at each end of the stomodseum (“ directives ”). In the species 
already examined there is a gradual tendency for the zooid to 
become elongated in the transverse axis, as a result of which the 
transverse mesenteries show a corresponding increase in breadth. 
In Girripathes the outline of the zooid is more or less rounded, but 
the insertion of the sagittal tentacles into the Dody wall instead of 
into the peristome interferes with the regularity. The diameter of 
the zooid in the sagittal and transverse axes is, however, practically 
the same, and the tentacles have a radiate arrangement. In Anti- 
pathella a slight elongation of the zooid in the transverse axis has 
the effect of making the tentacles appear in two rows of three each, 
parallel with the axis of the branch. On account of the oval out- 
line, there is in this genus a greater disproportion between the 
breadth of the transverse mesenteries, as compared with the “ di- 
rectives,” than is the case in Cirripathes. The increase in the 
length of the transverse axis is, however, not great, and the tentacles 
do not become removed far apart. In Parantipatlies i however, the 
transverse mesenteries become enormously elongated, so that the 
length in the transverse axis is three or four times that in the 
sagittal. The elongation has the effect of carrying the “ lateral ” 
tentacles further away from the stoinodsenm, so that they now 
appear clearly as three pairs some distance apart. The middle pair, 
as in other genera, are situated one at each end of the stomodseum, 
and the “ directive ” mesenteries are very narrow. In Parantipathes 
larix (Esp.) the peristome becomes somewhat depressed on each 
side of the oral prominence, so that the zooid presents indications 
of a division into three lobes, a central one containing the stomodseum 
and the proximal ends of all the mesenteries, and two lateral ones 
containing the greater part of the transverse mesenteries. It will 
be remembered that the reproductive elements are borne on the 
transverse mesenteries only, and in Parantipathes they are confined 
to those portions of them which are situated within the lateral lobes. 
It may be mentioned that in this genus the greatest diameter of the 
U. 
