HARD WICKE' S S CIENCE- G O SSI P. 



173 



terior region of the body. By the use of stains a 

 nucleus, in the form of a bent rod, can be brought 

 into view. Euplotes patella is one of the Infusorians 

 that have- chlorophyll corpuscles, and as they are few 

 in number they can be easily studied. Each consists 

 of two parts ; first, a green cup of chlorophyll con- 

 taining protoplasm enclosing a colourless ball of the 

 same substance. This is the structure of the green 

 bodies of most, if not all, of the Infusorians. 



It is obvious, from a glance at the figure, that 

 Euplotes is asymmetrical. Thus the nucleus is on the 

 left side, and the contractile space and food vacuoles 

 on the right, as viewed from the dorsal surface. 



2S. Before turning to the Peritricha we will notice 



Peritrichous Ciliata. 



We now come to a very interesting group of the 

 Ciliata, known as the Peritricha. These fix them- 

 selves by a stalk (a prolongation of their body) or by 

 a sucker-like arrangement. Vorticella is one of the 

 most common genera, and may be taken as a type. 

 There is a disc above the mouth fringed with cilia, 

 and a peristome or wall which surrounds the disc and 

 mouth, and which also bears cilia. The mouth is 

 situated below the disc, where this structure rises 

 highest. The oesophagus is sometimes ciliated, and 

 in certain species it is spiral. There is one large 

 contractile space and a nucleus. 



Fig. 109. — Slenlor viridis. aa, attached and expanded; B, free swimming; c, t, tail; «, segment of nucleus; ck, chlorophyll 

 corpuscles ; D, inyophan striation ; e, part of crushed specimen, to show protoplasmic network [ptl) and vacuole [v). In 

 all figures — c, cilia on expanded end; c', on body; d, disc; ch, chlorophyll corpuscle; «, segment of moniliform nucleus ; 

 oe, oesophagus ; p, peristome ; t, hyaline tail ; v, vacuole. A and B, 1 inch ; c and e, i inch ; d, i inch. 



Aspidiscus, which we have previously mentioned. 

 The life-history of Trichoda lynceus was worked out 

 by M. Jules Haime. The larval form is known as 

 Oxytricha (Fig. 10S, 2), and is heterotrichous. It is 

 somewhat oval in outline, with stiff bristles and cilia. 

 This becomes encysted, that is, it forms a cell-wall 

 round itself, and rests. When the resulting organism 

 escapes from the cyst it is hypotrichous, and was 

 called by Ehrenberg Aspidiscus (Fig. 108, 1) and 

 supposed by him to be a different organism. Like 

 Euplotes, Aspidiscus is furnished with a carapace, 

 from the under surface of which cilia are seen to 

 protrude. The figure gives a better idea of the form 

 of this curious organism than can be furnished by any 

 description. 



It must not be supposed that the Vorticellinse 

 are all permanently attached ; on the contrary I 

 have seen a detached vorticella, moving by the aid 

 of its long stalk across the microscopic field. Tri- 

 chodina can swim easily about by the aid of its 

 long basal cilia, and a Vorticella, recently produced 

 by fission and detached, swims about in a similar 

 manner. 



29. Stentor viridis (Fig. 109), when swimming 

 covered with its short cilia, resembles one of the 

 holotrichous Ciliata. It is the largest of the Ciliata, 

 and can be easily seen by the unaided eye. 



S. Miilleri (Fig. 1 10) of Ehrenberg, is of about the 

 same size as the chlorophyll-containing species, that 

 is, about one twenty-fourth of an inch long. 



