Structural Variation among the Diffiugian 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 

 Amoeba, exhibit a deternlinate 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 Amcpbce proper. And, lastly, the reproductive process is 

 the same as regards every known essential particular*. 



In the case of the freshwater Euglypliida, 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 Euglyphida differ 

 from the Amoebce . proper and Difflugida, inasmuch as their 

 ectosarc 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 DiSlugian tests are constructed of the most hyaUnc 

 materials, and specimens are obtained with the shghtest intermixture 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- 

 viduals 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 iii situ 

 after extrusion from the test ; whilst we may often assure ourselves that 

 objects within the test, supposed to be the 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 endosarc are indeterminate, of course admit- 

 ting of an equally satisfactory scrutiny, whether seen without or within the 

 test. 



Ann. is Mag. N. Hist. Ser. 3. Fo/. xiii. 15 



