PROTOPLASM AND SIMPLE ANIMAL FUNCTIONS 463 



Count the number of spontaneous contractions of the more or less 

 rhythmic smooth muscle of the stalk occurring in ten minutes. (See 

 Comptes Rendus Soc. de BioL, 1904, Ivi, p. 764.) 



The difficulty of defining individuality is finely shown by a comparison 

 of Vorticella and Zoothamnium. 



Expt. 6. The next specimen (to be studied with objective 3 first and 

 then with 5) is Stentor. This infusor is more clumsy and many times 

 larger than Vorticella, but has the same general mode of life. The con- 

 tractile stem in this case is surrounded with cytoplasm largely lacking 

 in Vorticella. The internal movements of Stentor are produced by the 

 simplest sort of muscular fibrillse longitudinally arranged about the 

 periphery of the thick body-stalk. The animal sometimes secretes a 

 delicate temporary cup-shaped shell about its foot, into which it quickly 

 withdraws. Some forms, however, are free-swimming only. 



Expt. 7. Euglena (viridis). This is a unicell of the flagellate sort 

 from 0.05 to 0.15 mm. in length. As its name implies, it is brightly 

 green and it is one of the organisms which sometimes color stagnant water. 

 This infusorian has a cell-wall (cuticle) note how it limits the shapes of 

 the animal as compared with Ameba. Its movements are, however, 

 various and characteristic. Euglena contains granules of some carbo- 

 hydrate. The chlorophyll is contained in one or more chromatophores 

 at the body-center. The bright red spot near the anterior (flagellated) 

 end is the eye a mass of pigment which can make the animal aware 

 only of degrees of light and shade. The flagellum arises from the bottom 

 of the mouth and draws food-particles into the gullet by the vortex 

 which it makes, and the same movements draw the animal through the 

 water. 



Draw all possible shapes of this minute protozoan and make notes of 

 its peculiar features. It is well illustrative of the unity of Nature that 

 the botanists claim Euglena as a plant-cell. 



Expt. 8. Brachionus. This little animal is common in the sand at 

 the bottom of ponds and fish-containing aquaria. It is one of the very 

 curiously shaped class of Rotifers (wheel-bearers). It is a multicell of 

 relatively complex organization, having an alimentary canal, a celomic 

 cavity, excretory organs, reproductive glands, a nervous system including 

 sense-organs, and muscles. It has also an elaborate body-wall. 



Make out the trochal disk from which is extended in front the long 

 proboscis-like organ with a prehensile arrangement at its end. See the 

 conspicuous eye of red pigment. Study the telescopic nature of the trunk 

 and especially of the long and slender " tail" with a pair of nippers at its 

 end for holding fast to bits of vegetal debris by a complex muscular 

 arrangement of claws. The tail in this species consists of four or five 

 segments completely telescoping when the animal retracts. Note its 

 inch-worm mode of travelling. 



Another rotifer, Philodina, inhabiting our aquaria in large numbers, 

 must not be confused with Brachionus. Its trochal disk is much more 

 conspicuous, and is oftener open. 



