8o LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



except that it secretes a brown hemispherical shell in which it lives and which 

 it carries on its back, so to speak, when it moves about. It is relatively common 

 in cultures. 



g) Flagellates: Organisms similar in appearance to the Euglena figured and 

 described in Hegner (p. 82) are not uncommon in cultures. Some are green, 

 some colorless, all possess long threadlike flagella as locomotor organs, although 

 these are often very difficult to see, as they are transparent. Flagellates are 

 best recognized by a peculiar swaying type of swimming movement, quite 

 distinct from the movement of ciliates. 



2. Multicellular organisms. These are readily distinguishable from Protozoa 

 by the presence of definite organs in their bodies. See Hegner (pp. 5-6) for 

 the general characters of the different phyla. One usually finds in cultures the 

 following types: 



a) The rotifers, or wheel animalcules (Phylum Trochelminthes) : These 

 extremely common animals are at once known by the presence of one or two 

 disks of cilia on their anterior ends. The constant movement of these cilia 

 produces the illusion of a rotating wheel. The ciliary apparatus can be folded 

 into the head. Other interesting features are the internal jaws, which keep up 

 a constant chewing movement, the jointed telescopic posterior end, often pro- 

 vided with one or more "toes" for clinging to objects, and the hard case, or 

 lorica, which often incloses the animal. The most common rotifer in cultures 

 is Philodina, which possesses a pair of "wheels." 



b) Roundworms or nematodes (Phylum Nemathelminthes), slender, cylindrical, 

 wormlike animals, pointed at both ends, without cilia, moving by violent alternate 

 curving and straightening of the body. 



c) Flatworms (Phylum Platyhelminthes) , slender flattened animals, moving 

 in a smooth gliding manner, due to the presence of cilia; with more or less 

 definite heads. Stenostomum is the commonest form, and often occurs in chains, 

 produced by fission. 



d) Chaetonotus (Phylum Trochelminthes?): This animal, possibly related 

 to the rotifers, resembles a ciliate protozoan. It has a slender flexible body, 

 possessing in front a rounded head region, followed by a short "neck," and at the 

 posterior end two pointed processes. The whole surface is covered with short 

 spines. 



e) Naids (Phylum Annelida), slender cylindrical worms, provided with 

 projecting bristles at regular intervals. The smallest ones belong to the genus 

 Aeolosoma, and have beautiful red, orange, or green spots. Some (Stylaria, 

 Pristina) have a long, slender, very active proboscis at the anterior end. Dero 

 is provided at the posterior end with an expansible hood bearing several ciliated 

 gills. Most of the naids are quite large compared to the other forms we have 

 been describing. They also occur in chains produced by fission. 



