340 NATURAL HISTORY. 



The sarcocle almost tills the interior, and is attached inside by threads of ectosarc to the hollow 

 sides and the base ; and it stretches to the mouth, whence it sends out about half a dozen simple or 

 branching pseudopods, and occasionally protrudes a large lump of its sarcode, usually soon retracted. 

 Thu food is, of course, taken in by that aperture, and the effete remnants are ejected thence at 

 the base of the pseudopods. Nucleus and contractile vesicle exist as in the naked Lobosa, 



XYIII. Hyalosphenia* is much like D'ifflugia, but has a transparent, structureless, bag-like 

 test, of a flattened-ovoid shape ; and gives out only a few linger-like pseudopods. 



XIX. Qnadrula\ is a very delicate and neat Diffluyia, with pear-shaped test, composed of 

 thin square plates symmetrically arranged. 



XX. Nebela is another Difflugian genus well known in its many " species," having a pear- 

 shaped, transparent, cancellated, membranous test, made up of circular, oval, narrow-rectangular, 

 and narrow-angular plates, occasionally more or less invested with extraneous particles, and some- 

 times crested, hirsute, or spiked. 



XXI. Heleopora \ is another closely related form, separated and named by Leidy because of certain 

 peculiarities in its plating, in its taking on sand at its rounded base, and its numerous pseudopods. 



XXII. Arcella, one of the commonest of the shell-bearing JRhizopods found in fresh water, may 

 be said to be like a flattish bell, a buckler, or a bun with a hole in its flat base, or a cap (Scotch 

 " bonnet "), each liable to various symmetrical squeezings of the sides and margin ; sometimes turned 

 up with sharp angles and long points. The shell is tough, not sandy, usually brown, and cancellated 

 with a delicately minute hexagonal pitting. The edge of the aperture, which is large, is frequently 

 turned inwards and upwards to some extent. The pseudopods are few and simple. 



There is also a terrestrial Arcella (A. arenarici), described by Dr. Greeff. 



XXIII. Centropyxis\\ is a common form, allied to Arcella, but not so symmetrical. Sub- 

 globular and depressed, sometimes spiky. Aperture not in the middle. Test sandy, as in Dijflwjia. 

 Pseudopods simple. 



XXIV. Cocliliopodium 9 ^ is a curious Amoeban, putting on very enigmatical appearances 

 according to its changes. It is bell-shaped, with a flexible test, sometimes expanding widely at 

 the aperture, which contracts or enlarges as the margin is bent in or out. The sarcode fills up and 

 adheres throughout to the inside of the envelope. Pseudopods delicate, sometimes forking. 



The above and other shelled Amoebans live in fresh water. 



XXV. Another group of fresh-water Rhizopods are those having thread-like branching 

 pseudopods (hence termed Rkizopoda filosa, or R. fittc/era**}, but otherwise the same general 

 constitution and form as the Shelled Lobose species. 



Their sarcode is generally like the endosarc of the Lobosa ; the delicate " pseudopods appear as 

 filaments of the finely granular protoplasmic basis of the sarcode ; " and their branches seem to 

 be only entangled in capturing prey, and not to blend or pass one into another. The tests are 

 egg-shaped, or like bags or flasks, &c., similar to those of the Lobosa, but generally more delicate, 

 and not so various in form, but always opening downwards, and sometimes excentric. 



PamphagiUfff Euglyi)ka,\\ and Trinema are some of the most common and best-known of 

 the Filosa. 



XXVI. Both the naked and the shelled Amoebina (Leidy's Protoplasta lobosa and P. filosa) 

 have their sarcodic contents encysted in a quiescent stage, the body having been purged of all effete 

 matter ; and the little globular mass ultimately breaks up into spherules, which are germs or spores in 

 all probability. Dr. Leidy notes that "From the researches of Mr. Carter |||| it would appear 

 that in Amoeba and Euglypha, representatives of the Lobose and the Filose Protoplasts, the 

 endosarc becomes resolved into nucleated cells, which are of the nature of ova ; while the nucleus 

 is resolved into gi-anuliferous, non-nucleated cells, finally breaking up into their constituent granules, 

 which are of the nature of spermatozoids."1iT 



* Greek, hyalos, crystal; spJien, a wedge. t Latin, diminutive of quailrus, square. 



1 Greek, helos(-eos) a bog ; jxra, a bag. Latin, area, a box. |1 Greek, centron, a prickle ; pyxis, a box. 



1! Greek, cocMos, a shell-fish with spiral shell ; pans, a foot. ** Latin, ,iilttm, a thread ; tjero, I bear, 



tt Greek, pumphar/os, all-devouring. JJ Greek, c u, well ; ffhipfie, sculpture. 



Greek, tri, three; ncma, thread. |l j| "Annals and Magazine of Nat. Hist.," 185G, vol. xviii., p. 226. 



HIT Greek, sperma, seed; zoon, an animal ; eidos, appearance. 



