24 INFUSORIA AND RHIZOPODA.. $$ 6, 7, 8 
CHAPTER I. 
EXTERNAL COVERING. 
§ 6. 
The Prorozoa are surrounded by a very delicate cutaneous envelopes 
which is sometimes smooth,” and sometimes covered with thickly-set cilia.‘ 
Generally these cilia are arranged in longitudinal rows ; ® but in Actino- 
phrys they consist of long contractile filaments of a special nature. 
CHAPTER II. 
MUSCULAR SYSTEM AND LOCOMOTIVE ORGANS. 
§ 7. 
With the Prorozoa a distinct muscular tissue cannot be made out, but 
the gelatinous substance of their body is throughout contractile. 
It is only in the contractile peduncle of certain Vorticellina, that there 
can be perceived a distinct longitudinal muscle, which, assuming a spiral 
form, can contract suddenly like a spring.” 
§ 8. 
Tus Visratite Oreans on the surface of Infusoria serve as organs of 
locomotion. j 
With many species they are found much developed at certain points, 
and are arranged in a remarkable order and manner. 
With Peridiniwm, a crown of them encircles the body; with Stylony- 
chia, they are quite long, and surround the flattened body like a fringe ; 
while the Vorticellina have the anterior portion of their body surrounded 
by retractile cilia, arranged in a circular or spiral manner. In Trichodina 
there is, upon the ventral surface, besides a crown of these cilia upon the 
back, a very delicate ciliated membranous border, which is attached to a 
ring which is dentated, and composed of a compact homogeneous tissue. 
With Trichodina pediculus this border is whole and entire; but it is 
broken or ragged with T'richodina mitra.” 
By means of this organ these animals swim with facility, or invade with 
skill the arm-polyps and Planaria.® With many Infusoria, the vibratile 
organs are situated at the anterior extremity of the body, as simple or 
double non-retractile filaments, which move in a manner to produce a vor- 
1 Euglena, Ameba, &c. 1 This Infusorium was discovered by me as a 
2 Trachelius, Paramecium, Nassula, &c. parasite in many Planarieae. 
3 Amphileptus, Chilodon, Opalina, &c. 2 Ehrenberg has entirely overlooked the ciliated 
1The peduncle is simple with Vorticella, but border of Trichodina pediculus, and bas regarded 
ramified with Carchesium. With Epistylis it is the stiff serrations of the ring as movable hooks. 
ot muscular, See “Die Infusionsthierchen,” p. 206. 
