ANATOMY AND THTSIOLOGY OP THE POEAMINIPERA. 173 
instances in which the same external contour presents itself 
under the porcelainous, the hyaline^ and the arenaceous aspects. 
But there is one feature in which they appear to differ. We 
find all the maturer shells of the hyaline type displaying a 
laminated structure (fig. 14), the laminge being added to the 
outer surface of the shell. The probable agency by which this 
has been effected will be better understood after describing 
the prevailing forms of the shells than now. Such laminm do 
not appear conspicuously in the porcelainous and arenaceous 
types, so far as I have observed; suggesting some probable 
difference in their modes of growth. 
In a very large number of the Foraminiferous shells, minute 
parallel unbranched tubes (fig. 14) pass through the shell- wall, 
estabhshing abundant communication between the exterior 
and interior of each shell. Occasionally these apertures are of 
considerable size, especially in young examples of some 
Rotalinac, but in others they are so minute and densely crowded 
together as to require careful observation for their detection. 
It is from these tubes that the term Foraminifera has been 
derived. They are not, however, the only means of commu- 
nication between the inner and outer shell-surfaces. In many 
of the hyaline types we have a much larger set of freely- 
branching tubes (fig. 15) distributed through the laminated 
shell- walls. These spread themselves through all the shell- 
walls, forming a free network where the shell is thick, as at 
its peripheral margin. In the latter localities, the canals are 
often of considerable size, giving off smaller branches, which 
penetrate even the thin septa separating the chambers. The 
tubes open abundantly upon the exterior of the shells, and, in 
a smaller degree, communicate with the internal cavities, being 
obviously designed to establish free communication between 
the two. 
It is very difficult to convey by words a correct idea of the 
various shapes assumed by the Foraminifera. The simplest 
is that which appears to be the embryonic starting-point of 
all the types, viz., a small atom of gelatinous sarcode inclosed 
in a hard spherical covering composed of one or other of the 
three elementary substances already described, the sphere 
having a single orifice in some part of its periphery. In the 
majority of instances this proves but a rudimentary state, from 
which higher and more complex structures are evolved by a 
budding process, but in Orbulina, Gromia (fig. 3), and the 
graceful Lagena (fig. 4), it is the ultimate condition, the 
single segments receiving no further additions. But this is 
unexceptional state, of things. Usually, additional segments 
are added, growing as buds or shoots out of the preceding one, 
each continuing attached to its predecessor by one or more 
