368 



NATURAL HISTORY. 



selves at pleasure. They increase in numbers by oblique fission, and a rudimentary mouth 

 fringe appears, and only in the part of the body which will require it after division. They live 

 in standing water among living and dead vegetation. One of the genus has blue colouring matter, 

 and another, in addition to its green chlorophyll, has spots of a brilliant scarlet, and a third is 

 black. The species of the genus Folliculina secretes a lorica, and the peristome opening occupies the 

 end of the projecting part of the animalcule (Fig. 24). Tintinnus lagenula is a type of a family of 

 this sub-order (Fig. 7). 



SUB-ORDER PERITRICHA. 



These Ciliata have the body smooth, except where there is a circular or spiral wreath of cilia in 

 front. Sometimes there is a second encircling wreath which may be at 

 the posterior part of the body, or at the middle. When the anterior 

 circlet of cilia assumes a spiral form the right limb of the part around 

 the mouth is mostly band-like and long. These animalcules may be 

 free swimming or attached in colonies, and in this case often forming 

 branching growths. They multiply by transverse and longitudinal 

 fission, and by conjugation. 



This very important sub-order is well divided into those families 

 which are free swimming, and those which are sedentary or attached. 



There are seven families of free swimmers, and in the first, con- 

 taining the genus Torquatella, the cilia around the mouth are replaced 

 by a vibratile collar. The second family has the animalcules 

 protected by a silicious covering or lorica, and the third has no 

 lorica, and there are retractile tentacules with the fringe of cilia in 

 the front. 



Halteria grandinella (Fig. 25) is the type of the fourth family, 

 and is a free-swimming globular animalcule, and it has the oral aperture 

 at one end, and associated with a spiral or sub-circular wreath of 

 large en-rate cilia. There is a zone of long hair-like setae around the 



body equatorially, and they enable the creature to jump in a most extraordinary manner. They roll 



themselves about, and suddenly leap backwards on to one side. There is a contractile vesicle and 



a spherical endoplast. The length is from ^-J-^th to y-J^th of an inch, and it inhabits pond water. 

 Another family has the animalcules pear-shaped ; the mouth is lateral, and there is a fringe of 



cilia around the body equatorially. Urocentrum turbo (Fig. 26) is the example, an:l the zones of cilia 



are in front, and equatorially, there being a terminal style, 



which is flexible, and enables the animalcule to adhere. 



The endoplast and contractile vesicle are very visible. It 



rotates like a top in the water, and moves forwards and 



backwards, and fixes itself, and spins backwards and 



forwards, so as to twist and untwist its stalk. The 



contractile vesicle has two or four sinuses, and the 



contraction expels the water visibly externally. They 



increase by transverse division. 



In the family Urceolaridse the wreath of cilia is 



near the adhesive disc-like posterior end, and the seventh 



family is peculiarised by its terminal setae, and a spinal 



adoral wreath of cilia. 



The family which contains the genus Dictyocysta is characterised by the possession of a beautiful 



helmet-shaped or bell-shaped silicious lorica, which is usually perforated so as to resemble a fine lace- 

 work. The species are from salt waters, are free swimmers in the Mediterranean and south-west 



coast of England. In their tests they closely resemble Polycistinse. 



The family Vorticellidse comprehends the Peritricha which are fixed during the greater part 



of their lives, and which are only temporarily free swimming. These are the " Bell Animalcules " 



Fig. 24. FOLLICULINA AMPULLA. 



(Modified after Stein.) 



A, Protruding from, and B, contracted in 

 lorica; c, Spirorbis shell with animal- 

 cules attached. 



Fig. 25. HALTERIA GRANDIXELLA. 



, Ventral, B, lateral, aspect; cv.contractile vesicle; n, nucleus. 



