142 
G. W. Lee — Trepostomata. 
III.—Development. 
Mr. E. R. Cumings has proposed 1 certain terms expressing successive stages of growth 
of the colony of the Bryozoa : the terms nepiastic, neanastic, ephehastic, and gerontastic 
being adjectives corresponding to an infant, adolescent, mature, or senile colony. Although 
these terms were originally applied to frondescent forms such as Fenestella , they can 
equally well be applied to other growth-shapes as met with among the Trepostomata. 
Examples of a trepostomatous Bryozoon in the phylastic stage, 2 or earliest stage 
capable of fossilisation, presumably exist in the British Carboniferous rocks, but at the 
outset one would be confronted by an almost insuperable difficulty in attempting to refer 
them to their proper systematic position. The youngest colonies that can safely be 
identified are in the form of patches encrusting various solid objects such as crinoid stems 
or shells. This stage marks the termination of encrusting growth in forms that produce 
erect zoaria, and can therefore be referred to the metanepiastic stage of Cumings. At this 
stage the zooecia are attached to a basal membrane, often described as epitheca , for which 
Prof. Gregory has recently proposed the more appropriate designation of epizoarium d 
The zooecia, in the thinnest crusts observed, differ in no way from the zooecia of the adult 
portion of the colony, except in point of size, being at first prostrate and thin-walled, then 
suddenly bending at a considerable angle and assuming the thickening characteristic of 
the Trepostomata. Acanthopores are likewise developed at this early stage, and tabulae 
are present in very thin crusts (plate xv., figs. 15, 16), though, owing probably to 
some accidental cause, not one is shown in the aspect depicted in plate xv., fig. 14. 
Bryozoa, like other organisms, sometimes skip certain stages of development, 4 but in 
the case of the ramose Trepostomata the metanepiastic stage could not be skipped, since 
an erect branching colony must necessarily have an expanded base of attachment. On the 
other hand, certain colonies may preserve for a long time the growth-shape characteristic 
of the metanepiastic stage, though actually an old colony possessing a thick “ mature ” 
region. A good example is the colony encrusting an Aclisina which accompanies the 
holotype of M‘ Coy’s Verticillopora dubia : the former is made up of zooecia actually larger 
than is the case in the latter. 
To the neanastic stage, which begins with the assumption of the habit of budding, 5 ' 
are referred colonies consisting of a crust throwing off small branches. An important 
point is that at this stage—at least, in the British -forms examined—the colony has the 
faculty of adopting indifferently two courses. In the one case the epizoarium raises itself 
2 Op. cit., pp. 54-56. 
3, p. 50. 
' 3 13, p. xx. 
4 3, p. 59 
Op. cit., p. 59. 
