ON THE GROUP PEOTOZOA. • 35 



to designate the peculiar semi-gelatinous substance composing the body 

 of these simple organisms. In the year 1835,* it was announced by this 

 observer, that the animal inhabitant of certain microscopic shells termed 

 Foraminifera by D'Orbigny,f though by hini placed among the Cephalo- 

 poda, agreed essentially in organization with the Amseba,' or Proteus ani- 

 malcule and other fresh- water forms allied thereto. It then became de- 

 sirable to separate these, as a group, from the true Infusoria; and accord- 

 ingly they were soon united into a class, under the name of Rhizopoda, 

 a term first introduced by M. Dujardin, but employed by him in not quite 

 so extended a signification.! , 



At length, in the year 1845, Von Siebold founded the modern sub- 

 kingdom, Protozoa, which he divided into two classes, Infusoria and 

 Rhizopoda§. JNo mention, however, is made by him of the Sponges. 



' Previously, in the year 1838, the name of Polycystina|| had been 

 given by Ehrenberg to a group of microscopic siliceous- shelled creatures, 

 evidently allied to the Foraminifera. Ehrenberg, it is true, entertained 

 very peculiar views of their affinities, and even sought to place them in 

 the neighbourhood of his Bryozoa. 



So early as 1828, Dufour had established the genus Gregarina^J for 

 the reception of certain minute parasitic organisms found by him in the 

 bodies of insects. In the year 1841, J. Midler described, under the 

 title of Psorospermias**, the contents of small rounded cysts occurring in 

 the cellular tissue of the muscles of a young pike's eye. Ten years af- 

 terwards, the existence of a curious relationship between these Psoro - 

 spermige and the Gregarinse of Dufour was ingeniously demonstrated by 

 Leydig.f f Doubts soon arose as to the position of these parasitic forms. 

 Creplin^ had suspicions of their vegetable nature ; the hasty observa- 

 tion of some phenomena in their development, which simulated the con- 

 jugation of the lower Algge, appeared, at first, to countenance this con- 

 jecture. Bruch§§, Leydig, and a number of other observers, regarded 

 them as Helminthes, or, at least, as transitory stages in the life-history 

 of these animals. But Kolliker, in a paper of great value, |||| brought 

 forward arguments which went far to prove, (1), that the GregarinaB 

 were true animals ; (2), that no good evidence had been produced to 



* " Observations nouvelles sur les pretendus Cephalopodes microscopiques," par M. 

 Dujardin, Ann. d. Sci. Nat., Ser. 2, torn. 3.— Zool., pp. 108 et 312. 



f In his " Tableau Methodique de la Classe des Cephalopodes," Ann. d. Sci. Nat., 

 torn. 7. 1826. The much older terra, Polythalamia, dates at least as far back as 1732. 

 See Breyn, " Dissertatio Physica de Polythalamis, nova Testaceorum Classe," 1732. 



X " Infusoires," p. 240. Also, " Recherches sur les Organismes inferieurs," Ann. 

 d. Sci. Nat., torn. 4, 1835; and "Observations sur les Rhizopodes et les Infusoires," 

 Compt. Rend., 1835. 



§ Lehrbuch der vergleichenden Anatomie, Wirbellose Thiere, 1845. 



|| See Abhand. d. Berlin Acad., 1839. 



U Ann. d. Sci. Nat., torn. 13, 1828, p. 366, et Ser. 2, torn. 7, 1837, p. 10. 



** Muller's Archiv., 1841, p. 477. 



ft Muller's Archiv., 1851, p. 221. 



jj Wiegmann's Archiv., 1842, p. 61. 



§§ Siebold und Kblliker's " Zeitschrift," 1850, p. 110. 



Illl Siebold und Kolliker's " Zeitschrift," 1848, p. 1. 



