_ LIFE HISTORIES OF THE PROTOZOA. 743 
dirt, and you have some idea of the general character of a 
Gromia.” 
A convenient division of the Rhizopods is into two groups, 
Foraminifera and Radiolaria. Schultze divides the former into :—- 
1. Nuda, or naked forms, such as Amoeba and Actinophrys. 
2. Monothalamia, forming a one-chambered shell, but with the 
animal undivided, living in the simple hollow of the shell. Fresh- 
water forms are Arcella, Difflugia and Gromia, while Cornuspira 
is a marine form. ; 
3. Polythalamia, with many-chambered shells; all marine. The 
three divisions are represented by (1) Acervulina, (2) Nodosaria 
and `(3) Miliola, Rotalina, Globigerina, Textularia, Nummulina, 
Polystomella, ete. 
The Rhizopods are divided by Heckel into 1. Acyttaria, or the 
one and many chambered Foraminifera; 2. The Heliozoa, repre- 
sented by Actinospherium (Actinophrys) Eichhornii, or sun-animal- 
cule; and 3. The Radiolaria. These last two groups he divides 
(a) into the Monocyitaria (represented by Cyrtidosphera, Thalassi- 
colla and Acanthometra, etc.) and (b) ihe a represented 
by Collozoum, Sphzerozoum and Collosphera. Heckel, who has 
studied these Radiolaria more than ia one else, though Johannes 
Miller gave us the first definite information about them, says that 
‘tin the lower forms they are allied to the sun-animalcules and 
Foraminifera, but the higher forms are much more highly devel- 
oped. They differ from both the Actinophrys and Foraminifera, 
in that the central part of the body is made up of many cells, 
and is surrounded by a strong membrane. This closed, more or 
less spherical *‘central capsule” is surrounded by a slimy layer 
of protoplasm, from which thousands of very fine threads radi- 
ate, and often branch out and anastomose: Among them are 
scattered numerous yellow cells, which contain starch granules.” 
(Whether these yellow cells are parasitic organisms, or belong to 
_ the animal, is not yet known.) Most Radiolaria are provided with 
lighly ee silicious frame-work, like the outer shell of a 
Chinese carved balls, the outer surface of which is studded 
- with spines; but both the form of the silicious box and the spines 
~ Varies greatly, as may be seen by a glance at the plate in volume 
III* (after J. Müller), illustrating the Polycystina. Some Radio- 
* Explanation of the plate. Fig. 1, Tetrapyle pees Fig. 2, Haliomma amphidis- — 
cus; Fi F e h ngispinum ; Fig. 4, Haliomma canthum ; Fig. 5, Haliomma? 
