SEOT. II 



PHYLUM PROTOZOA 



97 



their resemblance to the nematocysts so characteristic of Coelenterata 

 (vide Section IV.) is singularly close. 



Digestive Apparatus. Many parasitic forms (Fig. 72, 8, 17 ; 

 Fig. 76) have no mouth or gullet, and are nourished by absorption 

 of the digested food in the intestine of their host. The simplest 

 condition of the ingestive apparatus is found in Prorodon (Fig. 

 72, 1) and its allies, in which the mouth (mth.) is at one pole 

 of the ovoid body, and is closed except during the ingestion of 

 food, and the gullet (g.) is a short, straight tube. Such forms, 

 on account of the symmetrical disposition of their organs and the 

 want of differentiation of their cilia they are all holotrichous 

 may be considered as the lowest or least specialised of the Ciliata. 

 From them there is a fairly complete gradation to genera, like 

 Paramcecium, having the permanently open mouth on the left side 



l.Dictyocysl-a 



3.Thuricola ^.Ophrydium 5. S M chotricha 

 2.Pyxicola 



Fra. 73. Various forms of Ciliata. In 1 the shell alone is shown ; m. contractile fibre ; op. 

 operculum. (From Biitschli's Protozoa, after various authors.) 



of the ventral surface, at the end of a well-marked buccal groove 

 or peristome. Vorticella (Fig. 74) and its allies are peculiar in 

 having the edge of the peristome (per.) thickened so as to form a 

 projecting rim, and in the development of an elevated disc (d.) from 

 the area thus enclosed : the mouth (mth.) lies between the peri- 

 stome and the disc, and between it and the gullet proper (gull.) is 

 interposed a section of the ingestive tube called the vestibule 

 into which the reservoir opens, and which contains the anal 

 spot. In Nyctotherus (Fig. 72, 2) and some other genera there is, 

 instead of the temporary anal spot described in Paramcecium, a 

 distinct anal aperture (a.). 



Most of the Ciliata are naked, having no shell or other form of 

 skeleton ; but in a few forms the body is provided with a shell or 

 lorica, formed of a chitinoid material, and reminding us of the 

 VOL. I H 



