OF THE YOETICELLmA. 



593 



line, or joint. Upon Dytiscus marginalis. 

 1-430". 



Stein creates several additional species 

 of Opercidaria, and has entered into many 

 details respecting the structure of O. ar- 

 ticulata (xxx. 1, 2j. According to him, 

 the body is spindle-shaped or ovate-elon- 

 gate, and truncate before and behind. 

 The periston!, which is continuous with 

 the body, forms a simple terminal edge, 

 sometimes quite smooth, at others plaited 

 longitudinally. Similar plaits often occur 

 at its posterior half, when the animalcule 

 contracts itself. The disc of the rotary 

 organ has three circlets of cilia, is con- 

 tractile and changeable in form. The 

 oral ca-vity behind the margin of the 

 peristom is very wide and deep, ex- 

 panded as a capacious sac, from one 

 comer of which, posteriorly, the digestive 

 tube proceeds. It is lined internally by a 

 delicate hyaline membrane, which pro- 

 jects beyond the peristom like an upright 

 collar. At the base of the body is a dense 

 collection of granules, apparently of a 

 fatty character. The nucleus is horse- 

 shoe-shaped, and a round contractile 

 space lies near to the digestive tube at 

 its commencement. There is a pecu- 

 liar glandular-looking body on each side 

 of the oral cavity at the anterior part of 

 the body, the natm^e of which is not de- 

 tennined. When in a state of contrac- 

 tion the animal is thrown into annular 

 folds, the rotary organ completely re- 

 tracted, and the periston! closed over it 

 in a sphincter-like manner, the whole 

 body assui!!ing a spindle-shaped foiii!, 

 or, when cont!-acted to the uti!iost, a 

 pmform or orbicidar figure. Reproduc- 

 tion takes place by gemiiiation ; but fission 

 has not been observed : Stein believes in 

 the transfo!7nation of the animals into 

 Aeimtce, and the development froi!! 

 these of ciliated gemis (xxx. 3, 4). 



The length of the body of the largest 

 specimens, when extended, is 1-96"; 

 and the greatest ^vddth, at the i!!iddle, 

 1-216". The steii! is very variously 

 branched, and is less rigid and more 

 flexible than in other species. The 

 ti-ausverse lines or false joints are not 

 characteristic, and the longit!idinal stria- 

 tion is not always observable. 



0. herherina (Stein) (xxix. 4) = Epi- 

 stylis herheriformis (Ehr.).— Animalcides 

 outstretched elono^ated, cylindrical, 

 slightly contracted before and behind : 

 about 2i times longer than broad, with- 

 out reckoning the extruded rotary organ. 

 No separable peristom exists at the ante- 

 rior truncated extremitv {i. e. in technical 



phrase, it is obsolete); rotary organ 

 conrparatively shortly stalked, its disc 

 having a single whorl of cilia. Oral 

 cavity capacious, as in O. artkidata ; its 

 membranous lining mrdulating, and seen 

 with difficulty. An anal opening ap- 

 pears at the base of the oral cavity, not 

 far froi!! the orifice of the oesophagus. 

 Even when expanded, the body is sur- 

 rounded by thickly-placed anntilar folds, 

 which becoi!!e i!iuch more strongly pro- 

 nounced when it contracts itself.* The 

 siu-face of the body is covered by a very 

 firm, transparent, structm-eless mem- 

 brane, which can be isolated for exa- 

 mination without any special prepara- 

 tion, and is often left behind after death 

 as a distinct sheath or skeleton. Multi- 

 plication by gemi!!ation has not been 

 observed ; but fission is comi!!on. The 

 largest specimens were 1-190" in length, 

 and 1-570" in width. 



The fori!! of the stem is very variable, 

 for two similar specimens are scarcely 

 to be found ; yet in all, the animalcules 

 are supported at different heights, on 

 stems varying in length, and therefore 

 not corymbose. The stem, likewise, has 

 not the stiff, regular construction of 

 most Opercularice and Epistylkles, but is 

 generally curved outwards, and has at 

 variable distances transverse lines or 

 joints ; the extremity supporting the 

 animalcule is expanded. It is through- 

 out solid, colourless, and diaphanous, 

 and if at all striated longitudinaUy, is so 

 in a very faint manner. On aquatic 

 animals. Stein believes he has dis- 

 covered its Acineta (xxiii. 17, 20). 



0. LicMensteinii. — Body stout, short, 

 barrel-like, the length not being double 

 the width ; except in sparingly-branched 

 stems, the opposite ends are" little con- 

 tracted. The rotary organ is but slightly 

 elevated above the peristoi!! ; its stem is 

 short, thick, and al!!!ost cylindrical, little 

 exceeded in width by the disc surmount- 

 ing it, which has but a single circlet of 

 cilia. The men!brano!is process within 

 the oral cavity rises above the peristom, 

 is notched, thrown into longitudinal folds, 

 and, to all appearance, ciliated. The 

 nucleus is always short and oval or 

 round; its position varies; the con- 

 tractile space is circidar, in proximity 

 to the beginning of the digestive tube 

 or the oesophagus. The heap of fatty 

 corpuscles near the base is present, as 

 in many rigid-stem Vorticellina. The 

 maximum length is 1-190" ; and the 

 width 1-300". It differs from O. arti- 

 culata (xxx. 1, 2) by its round nucleus, 

 2q 



