1072 The American Naturalist. [December 
more than 200 gatherings in various localities of Europe, have 
brought me to the conclusion that many autonomous species of 
Rhizopods have acquired in their evolution and in independent 
ways the form pyriformis. Indeed, this simple and efficient 
shell is exactly the kind one would expect to be formed by an 
organism in its first stages of evolution from the amceba condi- 
tion to that of a testacean Rhizopod.' 
However it may be, if the following conditions are considered 
sufficient to determine a species : 
1. The general characters of the shell (form, size, structure, 
composition) are sharp and constant in a form A, though not far 
distant from those of other forms B, C, etc. 
2. In the state of copulation (conjugation) A is always seen 
together with A, and never with B or C, etc. 
3. In certain localities A is to be found alone, whilst B or C 
are not present. ĝ 
4. Intermediate forms between A and B, or C, etc., do not 
exist, or at least are very exceptional cases. 
If, I repeat, these characters, accumulating in one and the same 
form, are considered sufficient to make of that form a distinct 
species, then it would be easy to separate the Diffugia pyriformis 
Perty in a dozen at least of such autonomous species. 
Now I have observed at Caribou several different forms of Diff. 
pyriformis, and especially one that I found very abundant in 
several localities deserves a particular mention. With the typical 
form of the species, and built of angular grains of quartz, some- 
times with admixture of a few diatoms, its shell was remarkable by 
virtue of a large amount of brownish matter (oxide of iron), 
dissolved in a chitinoid magma, which generally formed a brown- 
ish substratum or inside lining to the shell. Now we must 
observe that in those species of Difflugia whose shells are nor- 
mally and essentially formed of sand particles, the proportion of 
1 At the same time, and whilst this explanation may be good in a general way, I am 
inclined to think that some of the forms or species so formed would still be in an unfixed 
state, and might be compared to such forms of vegetable life as Rosa, Rubus, Hieracium, 
which with their many varieties constitute the bliss of some, but the despair of most, 
collecting botanists. 

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A sad alta Wwe aaa iy S N 

