II* 
90 
hollow enlargements at the angles, which form their specific 
differences. So extensive is this effusion occasionally. O' 11 
I have known ten inches of cells in formation at one ti» ie | 
This form of growth fully explains the great length and tb« 
comparatively narrow extent to which this species attains- 
In some, and indeed in almost all cases, where the le»8* 1 
of the encrustation is great, tho longitudinal lines of c 
cells have a gently arched direction outwards. This ari*^ s 
from the manner in which the lateral increase is effected* 
and which may be termed the intercellular increase. 
the cells lie in their linear direction they gradually 
wider as they get more distant from the centre of growth' 
In this manner every eighth or tenth cell has so far increase _ 
in size, that two smaller one* are formed on its extrcnidv < 
these also increase in breadth, and hence a continued int*’ 1 " 
cellular enlargement takes place. The onter rows of cC 
are thus necessarily forced into the arched form, from tb eS ; 
internal wedges. This is the chief if not the only mode ^ 
lateral increase. If any obstruction is offered to the lope 1 
tudinal growth, such as an orifice in the frond or any ine ^ 
quality of the surface, the cells will take a circuit and m® 1 j 
on the other side. If however the polypidom be injur*- 
laterally, a small quantity of the pulp will be effused the 1 ®’ 
and the cells formed in it will be in the direction o! *•' , 
effusion, or at right angles to the original source. So t' 1 * 
the direction of the lines of the cells, is indicative of y 1 
point from which the pulp was effused. In the Hairy 
Mat ( Membranipora pilosa ) a lateral increase takes p* 3 ^ 
differently, but showing the same fact, that a calcare 0 "',- 
deposit takes place in the pulp, and is but a continuatio 11 0 
the same process that caused the effusion of the matrix. 
In the calcareous species, such as Cellepora puini c ° s ' 
Eschar a, Sfc., the formation of the cells is equally appa 1 '*' 0 ^ 
but changes occur in the character of the cells after they b 0t 
acquired their specific markings, which lend still furtb er .. r 
prove that the polypidorus are organic and liable to si** 1 * 
changes incident, to other organic structures. In the enc' 11 "^ 
ing calcareous species, the direction of growth appear*^ 
be diflused on all sides of the cells, and hence they gene* - ® ^ 
grow in circumscribed patches. After the pulp has ^ c ' y 
effused, the lime is deposited in a similar manner to that ‘ *" e 
crihed above, differing, of course, in some measure i* 1 , )e 
different species; in the Hairy Sea Mai for instance,. 
cells pass through a series ot changes, each ot wh* c 
is similar to the perfect cells of other species. Alt er 
pulp has been effused and the cells perfectly formed, ( 
calcareous deposit is not (row that time suspended, for !l . j. ( 
that period they considerably alter in appearance. The cc 
