THE LARGEST INFUSORIA. 



367 



Fig. 21. BUHSARIA 



TRUNCATELLA. 



(After Stein.) 



ci; Contractile vesicle; , 

 cndoplast curved, 



and in two long rows. These animalcules increase by several divisions across the body, and their 

 length is -., T -th of an inch. 



SUB-ORDER HETEROTRICHA. 



These Ciliata are free swimming or attached, naked or loricate, and the cilia form two widely 

 distinct systems ; those of the general surface being short, and those of the oral region large and like 

 cirri These oral cilia are either linear in their arrangement, or form more or 

 less spiral or circular series. The cortical layers are well developed, and some- 

 times contain parallel muscular fibrillae. 



The largest Infusoria are amongst this sub-order, which may be divided into 

 a family, the Bursariadse (Fig. 21), which has the cilia near the mouth confined to 

 the left border of the mouth groove, and into six other families which have the 

 mouth cilia in a spiral or circular series round the aperture. The first family 

 of this second group has free-swimming animalcules, and the fringe of cilia 

 around the oral aperture is confined to the ventral surface, and the anal orifice 

 is behind and at the end. Spirostomum ambiguum is the type of the family, 

 and is one of the largest animalcules, measuring th to th of an inch in length, 

 and being visible to the naked eye, "gleaming," Saville Kent remarks, " like 

 golden threads in the sunlight " (Fig. 22). 



When they are placed in clean water off the duckweed on whicli they 

 like to move, the body is long and filiform, has a tendency to twist itself and untwist, and the eye 

 is struck by the long contractile vesicle which occupies much of the hinder part of the body, 



and by the endoplast, which is long and 

 moniliform. The slit for the mouth is 

 surrounded by cilia. 



Another member of the family is 

 Condylostoma patens, found in sea water, 

 and -y-gth to T Vnd of an inch in length. 

 Its endoplast is moniliform and long, and 

 the anterior border of the body is rounded off, and flat in front, and the mouth groove is an angular 

 excavation occupying much of the ventral surface. There is an undulating membrane extending over 

 the whole length of the right side of the peristome border. The contractile vesicle is canal-like, and 

 breaks up into minor spaces (Fig. 12). 



A most important family has the trumpet-shaped 

 animalcules in it, whicli are usually found adherent by 

 their narrow bases, and often freely swimming. The 

 broad trumpet opening of these Stentoridse is the 

 region around the mouth, and the left-hand extremity 

 is turned in spirally, forming a funnel-shaped groove 

 whicli leads to the mouth. The right-hand limb is 

 usually raised higher than the opposite one, and all the 

 cilia around the mouth are large and strong. The 

 cilia of the rest of the surface are small, and arranged 

 in regular longitudinal rows, and there are occasional 

 setae. The endoplast is canal- like, and the contractile 

 vesicle is an anterior circular dilatation, which gives off 

 an annular branch that underlies the circumference of 

 the peristome. 



Stentor polymorphic (Fig. 23) is a large form, and 

 the colour is produced by the presence of rich green, 

 chlorophyll gi-anules. Its endoplast is moniliform, and 

 the whole trumpet is ^th of an inch long. It lives in 

 groups, and the stems of all are immersed in a mucus which they secrete and hold on by. When 

 swimming the shape is altered, and may be pear-shaped or top- shaped, and they fix them- 



Fig. 22. SPIROSTOMUM AMBIGUUM. 

 cr, contractile vesicle. 



(After Stein.) 



Fig. 23. STEXTOK POLYMORrHUS. 



