THE INFUSORIA 445 



spiral of Vorticellids are formed each by the concrescence of three rows of 

 cilia (Pig. 186, K, u.m.) ; in Olaucoma scintillans there is a " peroral " mem- 

 brane built up of five rows, an " endoral " membrane of ten rows of fused cilia 

 (Maier, 73). 



The membranellae of the adoral zone are formed each by the concrescence 

 of two transverse rows of cilia (Fig. 186, G, ml.). In some genera (Stentor, 

 Spirostomum) the basal rim of each membranella is continued down into the 

 endoplasm in the form of a fibrillar plate, triangular in form, with the apex 

 continued into a terminal filament, which is attached at its proximal ex- 

 tremity to a fibril running longitudinally, parallel to the row of membranellae. 

 The nature of this basal fibril has been much discussed ; it has been regarded 

 as a nervous element, co-cordinating the movements of the membranellae ; 

 Maier, on the other hand, regards the basal lamella and its terminal filament as 

 serving for the firmer attachment of the membranellae, and considers the 

 basal fibril to be a contractile element ; Schroder states that the basal fibril 

 is really a broad band, and believes its function to be purely mechanical ; 

 Schuberg rejects the nervous theory of the basal system of the adoral zone of 

 Stentor, but comes only to negative conclusions with regard to its function. 



The cirri of the Hypotricha are formed by concrescence of a tuft of cilia 

 arising from a number of basal granules which are arranged to form a basal 

 plate (Fig. 186, H, C.). The posterior ciliary ring of Vorticellids is composed 

 of " membranulae " (Maier), each formed by concrescence of a single row of 

 cilia, three in each row. The two circlets of Didinium are also membranulae 

 (Thon). 



Closely connected with the bases of the cilia in position, and with the 

 ciliary apparatus in their general arrangement, are the myonemes. The most 

 superficial study of the Ciliata suffices to convince the observer that these 

 animals have in many cases an extremely efficient contractile system. Such 

 forms as Stentor, Vorticella, etc., contract with such lightning rapidity that 

 it is almost impossible to kill and preserve them expanded ; the spasmodic 

 action of their contractile organs contrasts sharply with the slow contractility 

 of lower Metazoa, such as polyps. Trachelocerca, according to Lebedew (93), 

 contracts in an instant to one-twelfth of its length when expanded. 



In their primitive arrangement the myonemes run parallel to the rows of 

 cilia, immediately beneath the basal granules or close beside them (Fig. 186, 

 B, m.). In Stentor the myonemes are broad and band-like, and composed of 

 alternating light and dark portions (Fig. 186, J) ; they are lodged in canals 

 below the alveolar layer, running in the intervals between the "' ribs ' : or 

 pigmented strips of the body-surface ; the rows of cilia run above each 

 myoneme-canal, slightly to the side of it (Fig. 186, /). The myonemes run 

 the length of the body, from the foot to the adoral zone of membranellae. 

 At the extremity of the foot they bend inwards and form a cone or " foot- 



FIG. 186 continued : 



from a number of basal granules in a row forming the basal rim (b.r.) ; below 

 the basal rim is the basal lamella (b.l.), continued at its apex into the end- 

 fibril (e./.), which passes down to the basal fibril (&./.), seen cut in transverse 

 section : Z, zoochlorellse ; H, part of a section of the body of Stylonychia 

 histrio, showing two tactile cilia (t.c.) on the dorsal surface, and on the ventral 

 surface two cirri (C.), each composed of a fused tuft of cilia arising from a basal 

 plate of granules ; I, section of the body-surface of Stentor coeruleus, showing 

 the longitudinal myonemes (l.m.) lodged in canals (c.m.) between the pig- 

 mented " ribs " (p.) of the outer surface ; J, one of the longitudinal myonemes 

 of Stentor in surface view, showing the alternating light and dark portions ; 

 K, detail from a longitudinal section of Epistylis plicatilis, showing the two 

 undulating membranes (u.m.) of the peristome in transverse section, each 

 composed of three fused cilia arising from three basal granules (b.g.) fused 

 together ; from each basal plate arises a fibril ; the two fibrils join and become 

 continuous with one of the longitudinal myonemes running down the body 

 to the stalk. 



A after Schuberg (44) ; B H after Maier (73) ; /, J, after Schroder 

 (867) ; K after Schroder (865). 



