THE INFUSORIA 



177 



manner that, when they are put together; the serrations slightly over- 

 lap the straight edge of the next adjacent piece, thus leaving open- 

 ings for the protrusion of the cilia. The lower end is covered by 

 separate pieces, which open centrally for excretion. On the anterior 

 end, the mouth, crowned by a ring of large cilia, is protected by a 

 set of plates with teeth-like projections, which act somewhat like the 

 similarly arranged teeth of a sea-urchin. 



In a great many cases the outer body wall is marked by striations 

 of various kinds showing the lines of insertion of the cilia. A 

 typical example is shown in the membrane of 

 Holophrya, one of the Holotrichida(Fig. 91, A, 

 and 97, g}. Here the cilia are inserted in 

 regular lines which run from the anterior to 

 the posterior end. In other cases, as in Lem- 

 badion (Holotrichida), the cilia are inserted on 

 minute papillae, which lie in rows upon the 

 cuticle with more or less distinct furrows be- 

 tween them, thus forming secondary, but very 

 distinct, markings in addition to the primary 

 lines formed by the insertion points of the cilia. 

 That the striation is due to the ciliation can 

 be easily seen in cases where the cilia are 

 absent from one portion of the body and pres- 

 ent in others, as in many of the Holotrichida. Fig.$>4. Lacrymana coronata 

 The rows are not always straight, as in Holo- cu anc ? , Lach ' [ BUTSC LI : 1 



' 3 ' m, spirally wound rows of cilia. 



p/uya, but are variously changed through the 

 alteration of the axial relations. The most 



frequent variation from the primitive condition is the spiral arrange- 

 ment (e.g. Lacrymaria coronata, Fig. 94), where the course of the 

 cilia has become changed by the alteration in the position of the 

 mouth. A very curious type of striation is seen in DasytricJia 

 ruminantum (Schuberg, '88) (Holotrichida), where the striations do 

 not converge at the mouth as they do in the majority of forms, but 

 in a line above it. The exception is significant, however, as showing 

 the line of the shifting of the mouth, the path being marked by the 

 meeting points of the converging striae (Fig. 95). 



The external markings were early recognized by Ehrenberg, who 

 interpreted them as the insertion points of the cilia as described above. 

 Stein, however, held that the markings are invariably due to the pres- 

 ence of myonemes which form the insertion base of the cilia. Both 

 observers were right in part, for striations in some of the Heterotri- 

 chida and Peritrichida are due to the presence of myonemes, but in the 

 Holotrichida, where, with one or two exceptions (Holophrya, Prorodon\ 

 myonemes do not occur, the markings are unmistakably due to the cilia. 



