TRICHODINA STEINII (C. AND L.). 239 



(ring band) as a conspicuous feature of its "adhesive organ." 

 In this complex adhesive organ, with its velum, Louis Agassiz 

 (50) saw homologies between it and the details of an hydro- 

 medusa. Because of this he looked upon the Trichodina as being 

 the medusa of Hydra. Attempting to establish analogies may, 

 therefore, lead one into strange ventures. But a further homol- 

 ogy may be seen in the horny ring of the adhesive organ of 

 Trichodina Steinii. This ring is of a chitinous texture and lies 

 at the posterior extremity of the body of Trichodina. Faure- 

 Fremiet (05) studied the adhesive substance that Vorticella 

 elaborates when it fixes itself to a surface. He found that this 

 adhesive material was a "secretion chitineuse." If now the 

 reader will look at our figures 3 and 4, he will see that in the 

 free swimming Vorticella and Trichodina at the posterior end of 

 each of these ciliates is a region concerned with the secretion of 

 a horny material. In Vorticella the horny substance is the 

 adhesive material, whereas the homologue of this horny substance 

 becomes the horny ring or "striated ring band" of the adhesive 

 mechanism in Trichodinii Steinii. 



Perhaps a more interesting comparison may be drawn between 

 Vorticella and Trichodina than that based upon homologies. 

 This contrast presents itself in the polarity of the two protozoa. 

 Vorticella has its anterior-posterior polarity normal. When a 

 Vorticella moves about it swims with its peristome forward as 

 indicated by the arrow in Fig. 4. The careful studies of Jennings 

 (04) indicate that it is a matter of great importance to an animal 

 like Paramoscium that its peristome lies towards the line of travel. 

 To reverse this attitude would appear, therefore, to be a radical 

 change. This, however, is what has taken place in Trichodina 

 Steinii. These ciliates become quite active when their host is 

 placed under the compound microscope's light and creep about over 

 the surface of the host freely. In all cases they advance posteriorly 

 as they cling lightly to the surface of the host with their adhesive 

 organs. If the disturbance be continued long enough, they will 

 leave the host and swim off into the water. Even the free 

 swimming specimens travel posteriorly. When thus traveling, 

 they have the peristome closed and inactive while the velum and 

 horny ring are expanded (Fig. 3). There is thus a complete 

 reversal of polarity of this animal both when it creeps over a 



