ORGANISATION OF THE C1LIATA. 253 



radiate. Unlike the members of the last group, the so-called 

 " Hypotricha " are bilaterally symmetrical with flattened body and an 

 arched back. The latter is completely naked, for the cilia, which 

 are partly in the shape of stylets and hooks, are developed exclusively 

 on the ventral surface, on which the mouth is also found. With the 

 help of these appendages, the animals exhibit a regular creeping motion. 



All these groups, with the exception of the last, contain, besides 

 free-living forms, parasitic species, which infest both the higher and 

 lower animals. Thus the paunch and reticulum of the sheep and ox 

 harbour no fewer than six different species of ciliated Infusorians, 

 and that in such abundance and constancy, that they are always to 

 be found, along with the above-mentioned Monads, in countless 

 numbers in every individual. Five of these (species of Ophryoscolex 

 and Entodinium) are remarkable mail-clad forms with retractile organs, 

 and belong to the Peritricha ; the sixth (Isotricha intestinalis} is one 

 of the Holotricha. 1 Along with the latter we must include the 

 mouthless genus Opalina, which has, however, been hitherto observed 

 only in cold-blooded animals, but is very often found as constantly 

 and frequently 2 in the cloaca of the Batrachia, and especially of the 

 common frog, as are the formerly mentioned parasites in the ruminants. 

 Along with the Opalince, other heterotrichous parasites are found in 

 the frog, all which forms were referred by Ehrenberg to the great 

 genus Bursaria, but we now know that they belong to certain ex- 

 clusively parasitic groups (Balantidium , Nyctitherus) which are nearly 

 related to Bursaria, and which form along with them the family 

 of the Bursariese. 



To this family, and indeed to the genus Balantidium, we must 

 also refer the so-called Paramcecium coli, the only ciliated Infusorian 

 which has been as yet found in the human body. Other ciliated 

 forms have, it is true, been observed in men, in unclean wounds, 

 ulcers, &c., but always only free-living forms, which generally live on 

 putrefying matter, so that, in spite of their occurrence in this way, 

 they ought hardly to be reckoned among genuine parasites. J. Vogel 

 mentions among these forms Colpoda cucullus and Vorticella, 3 which 

 are both extremely common in putrid infusions. Wedl also mentions 

 a Bursaria (?), 4 but from the "flapping" motions of the lips of the 



1 Regarding these species see the statements of Stein (Lotos, Jahrg. ix., pp. 55, 1859, 

 and Abhandl. der kgl. Bohmischen Gesellsch., Bd. x., p. 69, 1860). In the colon of the 

 horse there very often occurs a hitherto but little known Infusorian, which, so far as 

 regards the nature of its cilia, might belong to the above-mentioned genus, Isotricha, 

 or Balantidium, and at any rate possesses a completely ciliated oval body. 



2 The parasitic Infusoria of the frog were detected even by Leeuwenhoek, " Op. omn., 

 Anat. et Contempl," t. i. p. 56, 1722. 



3 " Pathologische Anatomie," Th. i., p. 404, 1845. 



* " Grundziige der pathol. Histologie," p. 796, Fig. 195. 



