Part 18 (1/2)

In the figure given by Quennerstedt there are only 7 ventral cirri.

In the Woods Hole form there are 8, 7 of which are anterior, 6 of them about one central one. The eighth cirrus is by itself, near the base of the largest posterior cirrus. These cirri, in spite of their size, are easily overlooked and more easily confused, but by using methylene blue they can be seen and counted.

Aspidisca polystyla Stein. Fig. 57.

This species is similar to _A. hexeris_, but is smaller, very transparent, and without the spur-like process on the left edge of the carapace. The chief difference, however, lies in the number of a.n.a.l cirri. These are 10 in number and they are arranged obliquely as in the preceding species, with the largest one on the right and the smallest on the left. The ventral cirri are 8 in number, and are arranged in two rows, one of which, the right, has 4 cirri closely arranged, the other having 3 cirri close together and one at some distance, near the largest a.n.a.l cirrus. The peristome, contractile vacuole, and nucleus are similar to the preceding. Length 36; width 22.

[Ill.u.s.tration: Fig. 57.--_Aspidisca polystyla_.]

Stein a.s.signs only 7 ventral cirri to this species, but he also describes 2 very fine bristle like cilia (p. 125) and pictures them in figs. 18, 19, 20, and 21 of his Taf. III in the same relative position as my eighth cirrus. I am positive that cilia do not occur on the ventral face of this form, and that the characteristic cirri are the sole locomotor organs.

KEY TO FAMILIES OF PERITRICHIDA.

a. Peristome drawn out into Family _Spirochonidae_ funnel-like process; parasitic

b. Adoral zone and circlet of cilia Family _Lichnophoridae_ at opposite end. Adoral zone (one genus, *_Lichnophora_) left-wound. Parasitic.

c. Adoral zone a left-wound spiral. Family _Vorticellidae_ Attached or unattached forms.

* Presence at Woods Hole indicated by asterisk.

Genus LICHNOPHORA Claparede '67.

(Gruber '84; Fabre-Domergue '88; Butschli '88; Wallengren '94; Stevens 1901.)

Small or medium-sized colorless animals, extremely elastic and flexible. The anterior part, bearing the adoral zone, is round or oval in ventral view, and has a flat ventral and a highly arched dorsal surface. The posterior end of the animal is reduced to a stalk-like structure which is broadened at the extremity to form a sucking disk. The surface of this disk and the surface of the peristome may be brought into the same plane by the characteristic bending of the stalk portion. A ciliated girdle is placed at the edge of the sucking disk. A well-developed adoral zone incloses the peristome; it begins at the mouth on the left side and includes nearly all of the peristome in its left-wound spiral, the extremity approaching closely the end near the mouth. The macronucleus is a long-beaded structure, or it may be in several parts connected by strands (Gruber). The contractile vacuole is on the left side in the region of the mouth. Salt water.

Lichnophora macfarlandi Stevens. Fig. 58.

The body is elongate; oral disk variable in form, attachment disk clearly defined and constant. The stalk is very contractile and elastic, constantly changing in shape. When detached from the host the animal moves with a very irregular and indefinite motion. When attached it moves freely over the surface on its pedal disk. The latter is bordered by four membranes composed of cilia. A distinct axial fiber extends from the pedal disc to the peristome and gives off a number of branches. This fiber is a.n.a.logous to the myonemes in _Vorticella_. An indistinct longitudinal furrow can be made out occasionally. The nucleus is in 5 or 6 separate pieces, of which 1 is found in the pedal disk and 1 or 2 in the neck.

On the egg capsules of _Crepidula plana_; also reported upon annelids at Woods Hole.

Length 60 from disk to extremity of the peristomial disk.

[Ill.u.s.tration: Fig. 58.--_Lichnophora macfarlandi_.]

This form does not agree in all respects with Stevens's species, but the agreement is so close in other respects that I believe it can be safely identified as _L. macfarlandi_. The mode of life is different, and the macronucleus is different, there being from 25 to 30 fragments in Stevens's form and only 5 or 6 in the present one. There is, however, the same evidence of chain formation in both of them.

The length of the oral cilia in Stevens's form is 18 in fixed and 30 in living forms. In the Woods Hole form the cilia are not more than half that length.

KEY TO THE MARINE GENERA OF VORTICELLIDae.

Diagnostic characters: Attached or unattached forma of peritrichous ciliates in which the adoral zone seen from above forms a right-wound spiral. A secondary circlet of cilia around the posterior end may be present either permanently or periodically.