Structural Variation among the Difflugian Rhizopods. 217 
with the exception of a small area posteriorly, is devoid of granu- 
larity, and possesses no adhesive power. Hence the pseudo- 
podia do not coalesce unless during the inception of food. 
Again, the bodies of Difflugia and Arcella, as is the case in 
Ameba, exhibit a determinate anterior and posterior portion, 
the projection of the lobate or finger-like pseudopodia taking 
place only over the former region, whilst the latter serves, 
through an increase of the adhesive power over a small area, to 
furnish attachment to the fundus of the test interiorly. In 
both, the nucleus and contractile vesicle or vesicles, after dis- 
engagement from the test, are found to be identical in character, 
and to exhibit the same tendency to subdivision, at certain pe- 
riods of the creature’s history, that is witnessed on a larger scale 
in the Ame@be proper. And, lastly, the reproductive process is 
the same as regards every known essential particular*. 
In the case of the freshwater Huglyphide, although the diffi- 
culties of observation are somewhat increased in one direc- 
tion, owing to their more minute size, these are more than 
counterbalanced in another by their freedom from mineral 
particles, which usually interfere with vision ; and, with a little 
care, we are enabled to perceive that an absolute identity in 
the character of the soft parts pervades this group also. In- 
deed this identity would seem to have been recognized, inasmuch 
as the genera into which the species and their varieties have 
been constituted by different observers are distinguished from 
each other altogether by the shape, size, colour, and markings 
of the tests. Under a cautious examination of the sarcode- 
mass, we are enabled to perceive that the Kuglyphide differ 
from the Amebe proper and Difflugide, inasmuch as their 
ectosare is minutely granular, and possesses a decided degree of 
adhesive viscidity throughout the entire body, whilst their 
pseudopodia also exhibit a finely granular outline, are filiform, 
* Even when the Difflugian tests are constructed of the most hyaline 
materials, and specimens are obtained with the slightest mtermixture of 
extraneous matter, it is extremely difficult to trace out the appearances 
presented by the organs they enclose, with any approach to certainty. 
Indeed the attempt to do so is vain, unless we happen to meet with indi- 
yiduals the tests of which are constructed of mineral fragments flat enough 
and thin enough not to interfere materially with the passage of the rays of 
light. Under proper management, however, it is quite possible so to regu- 
late the action of the compressor as to keep the soft parts more or less in situ 
after extrusion from the test; whilst we may often assure ourselves that 
objects within the test, supposed to be tlie nucleus, contractile vesicles, or 
food-particles, are in reality so, by carefully watching their transit as they 
escape under pressure,—bodies like the sarcoblasts and crystalloids, the 
positions of which within the endosare are indeterminate, of course admit- 
ting of an equally satisfactory scrutiny, whether seen without or within the 
test. 
Ann. & Mag. N. Hist. Ser. 8. Vol. xiii. 15 
