92 SIDNEY F. HARMER. 
that Allman (1, pp. 8, 13) gave the name of “ ectocyst.” 
There is, however, a good deal of reason for believing that the 
arrangements are not quite so simple in calcareous Polyzoa. 
Ostroumoff (14) announced in 1885 that the use of silver 
nitrate demonstrated the evidence of an epithelial layer external 
to the calcareous skeleton in several genera of calcareous 
Polyzoa; and later (15, p. 12) expressed himself to the effect 
that in calcareous forms, such as Lepralia, the calcareous 
matter separated the ectoderm into two layers, one of which is 
outside the skeleton. Vigelius (22, sep., pp. 3, 4, pl. vi, fig. 24) 
describes and figures an extra-skeletal layer in an encrusting 
Cheilostome, and in a later paper (23) states that the skeleton 
is probably usually formed inside the ectoderm-cells. Pergens 
(17) finds that the skeleton of the calcareous forms examined 
by him is overlaid by a cuticle merely. 
The relation of the calcareous skeleton to the parts of the 
living body-wall appears to need further elucidation; but the 
condition found in Lichenopora makes it probable that, in 
that genus at least, there is more than mere ectoderm outside 
the calcareous layers of the upper surface of the colony. The 
cavities of the cancelli are probably morphologically parts of 
the body-cavity; and as such are no doubt surrounded by more 
than ectoderm. 
It appears to me extremely likely that the relations of the 
calcareous septa in Lichenopora may not be very different 
from those of the septa of a Zoantharian Coral, as shown by 
Koch’s well-known researches. The outer wall of the young 
funnel-shaped colony (fig. 3) is immediately derived from the 
body-wall of the metamorphosed larva; and it is of course a 
young condition of the basal lamina. All the septa which 
divide the zocecia, the alveoli, and the cancelli from one another 
are ultimately derived from the basal lamina; the first forma- 
tion of a young septum at the growing edge always appearing 
as an outgrowth from that layer (fig. 14), and other septa being 
always formed from pre-existing septa. 
I have obtained no evidence of the existence of soft tissues 
on the lower side of the basal lamina, and I do not think it 
