24 INFUSORIA AND RHIZOPODA. >§,§ 6, 7, 8. 



CHAPTER I. 



EXTKRNAL COVERING. 



§6. 



The Protozoa are surrounded by a very delicate cutaneous envelope, 

 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 Protozoa 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. 



The Vibratile Organs on the surface of Infusoria serve as organs of 

 locomotion. 



With many species they are found much developed at certain points, 

 and are arranged in a remarkable order and manner. 



With Peridmium, a crown of them encircles the body ; with Stylmiy- 

 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 TricJiodina pediculus this border is whole and entire; but it is 

 broken or ragged with Trichodina 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-reti'actile filaments, which move in a manner to produce a vor- 



1 Eug/ena, Amoeba, IfC. i This Infusorium was discovered by me as a 



2 Trackelius, ParamtBcium. Nassula, (fC. parasite in many Planarieae. 



3 Amphileptus, Chilodon, Opalina, 6fC. 2 F.hrenbers has entirely overlooked the ciliated 

 1 The peduncle is simple with Vorticella, but border of TricAodjna /^tajctt/us, and has regarded 



ramified with Carchesium. With Epistylis it is the stiff serrations of tlie ring as movable hooks. 

 not muscular. See " Die Intusionsthierchen," p. 206. 



