I40 PROTOZOA 



All these motile organs, with the exception of the preoral cilia, 

 pass into the pharynx ; but the adoral nienibranellae soon stop 

 short for want of room. There are some seventy memljranellae in 

 the adoral wreath. 



The rest of the ventral surface is marked by longitudinal 

 lines, along which the remaining appendages are disposed. On 

 either side is a row of " marginal cirrhi " {mc), which, like tlie 

 membranellae, may fray out into cilia, but are habitually stiff 

 spine-like, and straight in these rows ; these are the chief swim- 

 ming organs. Other cirrhi, also arranged along longitudinal 

 rows, with so many blank spaces that the arrangement has to be 

 carefully looked for, occur in groups along the ventral surface. 

 On the right of the peristome are a group which are all curved 

 — the " frontal cirrhi " (/.c). Behind the mouth is a second 

 group — the " abdominal cirrhi " {a.c), also curved hooks ; and 

 behind these again the straight spine-like " caudal " or " anal " 

 cirrhi {c.c), which point backwards. These three sets of ventral 

 cirrhi are the organs by which the animal executes its crawling 

 and darting movements. Besides the mouth there are two other 

 openings, both indistinguishable save at the very moment of 

 discharge ; the anus {aii) which is dorsal, and the pore of the 

 contractile vacuole, which is ventral. 



The protoplasm of the body is sharply marked off into a soft, 

 semi-fluid " endoplasm " or " endosarc," and a firmer " ectoplasm " 

 or " ectosarc." The former is rich in granules of various kinds, 

 and in food-vacuoles wherein the food is digested. The mode of 

 ingestion, etc., is described below (p. 145). The ectoplasm is 

 honeycombed with alveoli of definite arrangement, the majority 

 being radial to the surface or elongated channels running length- 

 wise ; inside each of these lies a contractile plasmic streak or 

 myoneme. The contractile vacuole {cv) lies in this layer, a little 

 behind the mouth, and is in connexion with two canals, an 

 anterior (e) and a posterior, from which it is replenished. 



The nuclear apparatus lies on the inner boundary of the ecto- 

 plasm ; it consists of (1) a large " meganucleus " formed of two 

 ovoid lobes {JSf, N), united by a slender thread ; and (2) two minute 

 " micronuclei " {n, n), one against either lobe of the meganucleus. 



Stylonijchia multiplies by transverse fission, the details of 

 which are considered on pp. 144, 147. 



The protoplasm of Ciliata is the most differentiated that we 



