3 8 INVERTEBRATE ANIMALS. 
with one another, and all surrounding themselves with a cal- 
careous covering. In this way we get ultimately a compound 
organism, composed of a number of little masses of sarcode, all 
permanently united to one another, and all enclosed in a com- 
mon shell. We get then, ultimately, such a form as Vodosaria 
(fig. 6, d, 2), which may be regarded as a good example of these 
so-called ‘‘compound” or “polythalamous” Foraminifera (Gr. 
polus, many ; thalamos, a chamber). The exact form of shell 
which is produced by this process of budding will depend upon 
the direction in which the buds are given off by the primordial 
segment. Ifthe buds are given off in a line, we get such a form 
as Vodosaria. If they are given off in a spiral direction, each 
succeeding segment being a little larger than the one before it, 
and the coils of the spiral all lying in one plane, then we get 
such a shell as Déscordina (fig. 6, c). This is one of the com- 
monest forms of shell amongst the Foramdnzfera, and it is often 
called the “nautiloid ” shell, from the close resemblance which 
it bears in shape to the well-known shell of the Pearly Nautilus. 
It was, in fact, this external similarity which induced the older 
naturalists to place the Foraminifera amongst the Mollusca in 
the neighbourhood of the cuttle-fishes. There are numerous 
other types of shell, all of which can be referred to the manner 
in which gemmation is carried on by the primordial segment ; 
but the two forms above mentioned may be taken as sufficient 
examples. It may be mentioned, however, that there are forms 
in which the new segments are added in a very irregular man- 
ner, and the resulting colony has no very definite shape, as in 
Globigerina (fig. 6, /). 
AFFINITIES OF THE FORAMINIFERA.— In spite of their beautiful, and 
in many cases complex, shells, the anatomical structure of the Foramini- 
Jera is so simple that it may fairly be questioned whether in a systematic 
arrangement they should not be placed at the bottom of the whole sub- 
kingdom, Protozoa. Perhaps the nearest relatives of the Foraminifera 
are the Polycystina, a group of organisms which we have yet to consider. 
These differ from the Foraminifera in little or nothing, except that the 
shell is composed of flint. The /oramznzfera are also clearly related to 
those forms of the Ameba which possess shells, such as Difiugia. The 
sarcode-body of Difzgia, however, contains a nucleus and a contractile 
vesicle, and the pseudopodia are thick and blunt, so that the differences 
are sufficiently weighty. There are also very interesting points of re- 
lationship between the Foraminifera and the sponges, which cannot be 
touched upon here. A few words, however, may be said on the physio- 
