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Show ON CLASSIFICATION. 82 . d tl e J. nteaumen t of certain Turbe. llartta, an<1 si1nilar weapons, an . 1 . . 0 'l'"'d with bodies wln0h seem to f In~'usor1,a, JS provtc e even o some '.! . • ·1 . ch· .. raeter. 1 tl r dissnni ar ~ ] I be of a not. a toge le irculatory organs, un ess t 10 No Cool en terate possesses a~ty c f the body can be regarded . 1. th general cav1 ·Y 0 cilia winch Ine e h s at present, been clearly Ina<1 e d nervous systenl a ' . as such; an a II . _ 1. 1 Ot ornhora et e ·ts central nut. s occupies a out only 111 t 1e en J.v 1.·1r · tl t I·n whi h the principal masses 1 · ry un I ,e 'a Position wlnc I IS ve , found in other invertebrate l . ous system ar o . . . of the centra n~rv tl at side of th body whiCh JS dla-auimals, being situated upon J d to the mouth. metrically opposet sw. n our 1t now ledo·e of the nervous apparatus o · Whatever ex en d not improbably will, receive from f tl Crolenterates may, an ,_ 1 h' t o le . t . ·ators t 1l e posi· t·IV e chca racters afforded uy t 10 IS o• - futu. re In ves ,Ig ' . b t e and tho free opening of thou 1 f, t . of the1r su s anc , c logwa ea ures 1 . t the general cavity of tho body, arc such alimentary cana In ° b ]~ 1- 110·clom as sh<ll'l)]y defined and t them as a su - ' ' . adse vtooi ds eopfa rtraa en si. tw. na'1 !.rO r• ms as that of the Vertebrata, fronl tho c. f 1 A ·mallGno·dom. rest o. t ~e di~l~ulties st:nd in th . way of any satisfactory ?roup- . Gfr etha e reman. n.n g. c] as ses ' if we are detonuined to remadin truel Ing o . . 1 tl t tl d finition of a group shall hoi gooc to the pnnmp e la 1 f th · a 1)rin-b . f' that groUI) and not o any o I ,- f all mem ers o ' 'fi t' o. 1 hich lies at the foundation of all sou~d cla .sl ca Ion ... mp eI nw po sessJ. ng '1' s locomotive and Ingestive organs ' m CI ta, a . 1 l . . . 1 a contractile water r c ptacle wit l cana s bemg p~ovl~~d w~~ (in some cases at any rat') into the substance proceeding r~m I . . nden. to become ncystecl and assume of the_ body; ~~-t:e~~! INFU, ~RIA undoubt dly exhibit analogies a ~·ehstlnl g leon l Aw n~uloida ·uch us th Tu?·bella1'·ia, Rotzjm·a, and w1t t 1e ower ' Trmnatoda. . r )]'(·sent knovvlodge But the entire aLsenc ' o far as ou. l . f t] e gullet th b ·upt t rnnnation o · 1 goes, of a nervous . ysteiTI' e. a r l tllo v ry peculiar cha- 1 · fl 'd r odic mass anc in a centra senn- ui sa. . ans 'of the Infusm·ia, separate racters of the reproductive mg< ' · t me not 'd 1 from the Annuloida, tho1lgh lt seems o . . them Wl e y h reafter bo considerably dJD11- improbable that the gap may ·b llar1·a. nished by observation of the lower forrns of T1.M e rl'HE JNFUSOlUA ..-\ ND PROTOZOA. 83 At present th(. In.fwwria. are nsnfllly regard cl as forming part of th sn.n1e sub-kingdom as the Spongida, Rh1'~opoda, and Gregarinida, and as closely allied to th m. Dut., so far as I an1 aware, no definition can bo framed which will yi lcl c•.haractcrs at once connnon to, and distinctive of, all those four group ; while recent discoveries toncl to widen so greatly the hiatns between th Injtttsoria and the other three classes, that I gr atly doubt if tho sub-kingdom PnoTOZOA can be retained in its old sen o. But if the Infusoria be excluded from it, tho remaining groups, notwithstanding the imperfection of our knowledge regarding some of them, exhibit a con. iclerahle co1nn1nnity of partly negative and partly positive characters. Tho Spongida, Rhizopoda, an l Gregarinida, in fa ·t, are all devoid of any definite oral aperture; a eonsiderable extent, and smnetilnos tho whole, of tho outer surface of the body acting as an ingestive apparatus. Furthermore, the bodies of these aninlal , or the constituent particles of tho c01npound aggregation , such as the Sponges, exhibit ineessant changes of form-the body wnll being pushed ont at ono point and drawn in at another -to su('h an extent, in some cases, as to give rise to long lobate, or :filamentous, processes, which are termed "pseudopodia." Finally, ~til these classes agree in the absence of any welldefined organs of reproduction, innervation, or blood circulation. In my first lecture upon Classification, I passed very briefly over the class Rhizopoda, intending to return to the discussion of its limits, and of the value of its subdivisions, when discussing the subdivisions of classes generally. But as time will not permit me to enter at any length upon the greater part of this branch of my subject, I will content myself with briefly stating the conclusions at which I have arrived from a careful study of the extant literature of the subject, cmnbined with son1e old investigations of my own. It appears that three, or perhaps four, types of structure obtain among the Rhizopoda- 1st. That of the Am{Ebm-Rhizopods with usua.lly short pseudopodia, a nucleus, and a contractile vesicle. 2nd. That of the Foraminifera-Rhizopods devoid of nuclei • G 2 |