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.

1. Posterior ciliated girdle 3 permanent around an attaching disk

2. Posterior ciliated girdle, 4 temporary during motile stage

3. Body cylindrical:

(a) With ring of stiff bristles Genus _Cyclochaeta_ above the ciliated girdle

(b) Without accessory ring of Genus _Trichodina_ bristles; with velum

Body conical; general Genus _Trichodinopsis_ surface ciliated

4. No test and no stalk Genus _Scyphidia_

5. No test; with stalk containing 8 contractile thread

6. No test; with stalk but without Genus _Epistylis_ contractile thread

7. With a test; with or without Genus *_Cothurnia_ a stalk

8. Individuals solitary Genus *_Vorticella_

Individuals colonial; Genus *_Zoothamnium_ entire colony contractile

Individuals colonial; parts Genus _Carchesium_ only of the colony contractile

* Presence at Woods Hole indicated by asterisk.

Genus VORTICELLA (Linnaeus 1767) Ehr. '38

(Bell Animalcule Leeuwenhoek 1675; Ehrenberg '38; Dujardin '41; Stein '51; Cl. & Lach. '58; Greeff '70; Butschli '88; Kent '81; Stokes '88; etc.)

Medium-sized ciliates of general bell-like form. They may be colorless, or yellow and green through the presence of Zoochlorella.

When not contracted, the peristome end is widespread, rarely narrowed. The adoral zone and peristome agree with the details given in the family characteristics. The chief character is the attachment of the posterior end by means of a single, longer or shorter, stalk, which contains a highly contractile thread easily distinguished in the living animal. Another character is the absence of colony formation. Contractile vacuole, single or double, usually connected with a sac-like reservoir. The macronucleus is invariably long and band-formed, with attached micronucleus. Fresh and salt water.

So many species of _Vorticella_ have been described that the task of collecting data and of arranging the synonyms is extremely irksome and difficult. Stokes enumerates 66 species, inhabiting fresh and salt water, and several other new species have been added since his work. I am impressed with the fact that new species have been created without proper regard for the manifold variations which nearly all of the _Ciliata_ show, and I believe the 66 species might be safely reduced to 12 or 15.

Vorticella patellina Muller. Fig. 59.

Body campanulate, widest at anterior border, from which it tapers directly to the pedicle. The diameter of the peristome is a little larger than the length of the body. The ciliary disk is but little elevated. The cuticle is not striated and the body plasm is quite transparent. Length 52.

[Ill.u.s.tration: Fig. 59.--_Vorticella patellina_.]