116 ON THE STRUCTURE OP PROTOPHRYA OVICOLA. 



upon an egg-capsule 350 micra in diameter apparently in adaptation to this sub- 

 stratum upon which they are habitually found. The form is quite constant in pre- 

 served material and is not subject to great change in living individuals. The only 

 irregularities in the otherwise perfect symmetry of the animal are those caused by 

 the contractile vacuole which lies near the posterior end. When this is at diastole 

 it causes a slight swelling in the dorsal outline near the posterior end (Fig. 2). 



Protophrya is a small ciliate, the length of preserved individuals varying from 

 88 to 102 micra, the width from 71 to 77 micra, and the thickness (total dorso-ventral 

 extension) from 30 to 35 micra. 



The body is ciliated throughout, and the cilia are of the same size everywhere 

 excepting along the margin of the ventral face, where they are somewhat longer (Fig. 

 2) and form a sort of peripheral fringe. They are very fine and closely set and are 

 well preserved in material killed in Flemming's fluid. The cilia are arranged upon 

 the surface of the body in meridional rows very closely set, which give a fine striation 

 to the pellicula. These striae are longitudinal as a rule, though in much contracted 

 specimens a very slight spiral torsion may be detected. This distribution of the 

 cilia is similar to that in most holotrichous ciliates, but the meridional lines are closely 

 set, more so even than in any other Opalinidse. There are about forty of these striae 

 on the dorsal surface and approximately twenty-five on the ventral. The distance 

 between them is but little more than two micra. This is much less than in any other 

 members of the family as figured by Schewiakoff ('96). Even in Opalinopsis sepiolse 

 (Foettinger, '81) they are three micra apart. It appears that this close-set and 

 abundant ciliation is an adaptation to the habitat of the animal, a structural provision 

 for rapid change in the surrounding medium. It lives in the secretions of the oviduct 

 which are not subject to such regular and frequent change as are the contents of the 

 intestine, the organ in which other members of the family, excepting Opalinopsis, 

 are found. In Opalinopsis sepiolse the lines of cilia are closely set, but this species 

 is also found where the need of rapid change of the medium is great, in the liver of 

 Sepiola. All members of the family Opalinidee are endoparasites, and all are more 

 or less marked by the very fine and abundant ciliation which may be an adaptation 

 to the mode of life. In Opalinopsis sepiolse and in Protophrya we find a maximum 

 development of this ciliation coinciding with parasitism in organs in which the nature 

 of the surrounding medium calls for more rapid change to facilitate the removal of 

 the waste products of respiration and excretion. 



The distinction between ectoplasm and entoplasm in this species is somewhat 

 similar to that in other holotrichous forms. The ectoplasm (Fig. 1, ec'pl.) consists of 

 a pellicula (Fig. 4, pell), an alveolar layer (st. ah.), and the cortical plasma (pi. ctx.). 



