MONOCELLULAR ANIMALS-THE PROTOZOA 



135 



the naked eye. In fact, when first observed, 

 it might be mistaken for a tiny worm be- 

 cause of its apparent crawHng movements. 

 Another large form, Stentor (Fig. 7-27), 

 vase-shaped and colored a beautiful green- 

 ish blue, is a spectacular sight for the mi- 

 croscopist. 



This order also includes several species 

 in which the long cilia are fused into stiff 

 bristle-like org-anelles called cirri. Cells of 

 this type are flattened dorso-ventrally and 

 seem to use their cirri in "walking" along 

 the substratmn. One of these is Stylotiichia 

 (Fig. 7-27), which is about the size of 

 Paramecium but whose actions are quite 

 different. It moves along in a jerky fashion, 

 darting forward and backward, and some- 

 times crawling along on the bottom. Pro- 

 fessor C. V. Taylor, working with a closely 

 related ciliate, Etiplotes, some years ago, 

 was interested in how this cell controlled 

 the cirri in locomotion. With the use of a 

 delicate dissecting instrument he was able 

 to cut the tiny fibrils that connect each of 

 the cirri with the others. Such an operated 

 animal lost control of its cirri and was un- 

 able to coordinate its movements sufficiently 

 to move in any one direction. Thus he dis- 

 covered that even this tiny animal possesses 

 some kind of coordinating system resem- 

 bling the nervous system of higher forms. 



Ciliates belonging to the order Peritricha 

 have their cilia conspicuously arranged in 

 the anterior region. Most of these forms 

 are vase-shaped and many are stalked. 

 Common examples are Carchesium (Fig. 

 7-27) and Vorticella (Fig. 7-28). Of the 

 two, the latter is more common and is 

 familiar to anyone who has persisted in ex- 

 amining stagnant water under the micro- 

 scope. It was seen and described for the 

 first time by Anton Leeuwenhoek in Hol- 

 land during the seventeenth century (Fig. 

 7-29). Vorticella is usually attached to the 

 substratum by means of its contractile stalk. 

 When disturbed or sometimes for no ap- 

 parent reason, it suddenly contracts and 

 at the same time the cilia around the 



Fig. 7-30. Plastic model of a suctorian {Ephelota 

 coronata). 



funnel-shaped mouth disappear and the 

 entire cell rounds up into a ball. Shortly, it 

 emerges again and starts its oral (mouth) 

 cilia beating so that food particles floating 

 by are wafted into its mouth. 



A peculiar group of Protozoa, the Stic- 

 toria (Fig. 7-30), are usually considered as 

 belonging to Ciliophora because they 

 possess cilia during the young stages, al- 

 though they are absent in the adults. In 

 their place these animals possess long and 

 numerous "tentacles" which are used in 

 capturing food (other Protozoa). Like 

 Vorticella, the suctorian has stalks and is 

 sessile most of its life. 



From this cursory survey of the Protozoa 

 one is impressed with the tremendous diver- 

 sity of form and habits of life that are avail- 

 able to a group of animals even though con- 

 fined to one cell. Think of the much greater 

 opportunity for diversity when cells are 

 aggregated into masses. Our course now 

 is to study representatives of succeeding 

 phyla where each is more complex than tlie 

 preceding, finally terminating with the most 

 complex of all animals, man. This great and 

 wondrous story should be followed with 

 keen interest because it is the way life 

 came to where it is today on this earth. 



