Chapter XI: Cercaria

Vermis inconspicuus, pellucidus, caudatus. An invisible pellucid worm with a tail.

124. CERCARIA GYRINUS. C. rotundata, cauda acuminata. Round cercaria, with a sharp tail.

It has a white gelatinous body, without any traces of intestines; the fore-part somewhat globular, the hind-part round, long, and pointed; sometimes it appears a little compressed on each side. When swimming, the tail is in a continual vibration, like that of a tadpole. It seems very similar to the spermatic animalcula.

125. CERCARIA GIBBA. C. subovata, convexa, antice subacuta, cauda tereti. Somewhat of an oval shape, convex, the fore-part rather acute, the tail round.

It is a small animalculum, gelatinous, white, opake, and without any visible intestines; the upper part convex or gibbous; many of them were found in infusions of hay, as well as of other vegetables.

126. CERCARIA INQUIETA. C. mutabilis, convexa, cauda lævi. Plate XXV. Fig. 31 and 32. Changeable convex cercaria, with a smooth tail.

This animalculum so often changes the form of its body, that it is not easy to describe it; it is sometimes spherical, sometimes like a long cylinder, at other times of an oval figure, white and gelatinous; the tail is filiform and flexible, the upper part vibrating vehemently; no visible viscera; a pellucid globule may be observed at the base, and two very small black points placed near the top at _d_, Fig. 32; whether they be eyes to the animalculum is not known. It was found in salt water. _a_, Fig. 31, the body; _b_, the tail.

127. CERCARIA LEMNA. C. mutabilis, subdepressa, cauda annulata. Plate XXV. Fig. 33, 34, and 35. Mutable cercaria, somewhat flattened, with an annulated tail.

This animalculum varies its form so much, that it might be mistaken for the proteus of Baker, though, in fact, it is totally different. The body sometimes appears of an oblong, sometimes of a triangular, and sometimes of a kidney shape. The tail is generally short, thick, and annulated, but sometimes long, flexible, cylindric, and without rings; vibrating, when stretched out, with so much velocity, that it appears as it were double. The intestines are not very distinct; a small pellucid globule, which Müller supposes to be its mouth, is observable at the apex; and two black points not easily discovered, he thinks are its eyes; sometimes it draws the tail entirely into the body. It walks slowly after taking three or four steps, and extends the tail, erecting it perpendicularly, shaking and bending it; in which state it very much resembles a leaf of the lemna. Fig. 33, _a_, the body rather spherical; _b_, the tail. Fig. 34, _c_, the triangular body; _b_, the tail. Fig. 35, the body extended; _e e_, the eyes; _f f_, the intestines; _g_, a large vesicle; _h_, a smaller one.

128. CERCARIA TURBO. C. globulosa, medio coarctata, cauda uniseta. Plate XXV. Fig. 30. Globular cercaria, the middle contracted, with a tail like a bristle.

Partly of an oval, and partly of a spherical shape, pellucid, and of a talky appearance. It seems to be composed of two globular bodies, the lowermost of which is the smallest; this figure is occasioned by the contraction at the middle. There are two black points, like eyes, even with a transverse line which crosses the upper part of this little creature; several large globules may also be discerned; the tail is sometimes quite straight, sometimes turned back on the body. It is to be found among duck-weed.

129. CERCARIA PODURIA. C. cylindracea, postice acuminata subfissa. Plate XXV. Fig. 36 and 37. Cylindric cercaria, the hind-part sharp and somewhat cloven.

It resembles the young ones of the podura[126] which live among the lemnæ, is pellucid, and appears to consist of a head, trunk, and tail; the head resembles that of a herring; the trunk is cylindric, replete with black spiral intestines, and appears more or less extended, at the will of the animal; nothing is to be discovered in the hinder-part. The tail most commonly appears to be divided into two bristles. The intestines are in a continual motion when the body moves, and by reason of their various shades give it a very rough appearance; some lateral hairs or cilia are likewise to be perceived. When it moves, it revolves at the same time as upon an axis. It is to be found in November and December, in marshy places that are covered with the lemna. Fig. 36, _a_, the head; _b_, the trunk; _c_, the tail; _d_, with one point; it is seen at _e_, Fig. 37, with two points; _f_, the hairs on the side.

[126] A genus of insects of the order of aptera. Linn. Syst. Nat. p.
1013.

130. CERCARIA VIRIDIS. C. cylindracea mutabilis, postice accuminata fissa. Cylindrical cercaria, mutable, the lower end sharp, and divided into two parts.

This animalculum in some of its states considerably resembles the last, but has a much greater power of changing its shape. It is naturally cylindrical, the lower end sharp, and divided into two parts; but it sometimes contracts the head and tail so as to assume a spherical figure, at other times it projects outwards. It is found in the spring, in ditches of standing water.

131. CERCARIA SETIFERA. C. cylindracea, antice angustior, postice acuminata. Cylindric cercaria, the fore-part smallest, the hind-part pointed.

This is a small cercaria, the body rather opake, and of a round figure. The upper part is bright, and smaller than the rest; the trunk is more opake; the tail sharp, and near it a little row of short hairs. It has a slow rotatory motion. It is found in salt water, though but seldom.

132. CERCARIA HIRTA. C. cylindrica, antice subtruncata, postice obtusa, bimucronata. Cylindrical cercaria, the fore-part somewhat truncated, the lower part obtuse, finishing with two small points.

A cylindrical opake animalculum, with two small points at the lower end, moveable, yet rigid, and placed at some distance; when in motion, the body appears to be surrounded with rows of small hairs separated a little from each other. It was observed in salt water.

133. CERCARIA CRUMENA. C. cylindraceo-ventricosa, antice oblique truncata, cauda lineari bicuspidata. Cylindrical, ventricose cercaria, the fore-part obliquely truncated, the tail linear, terminating with two diverging points.

The body is ventricose, cylindrical, thick, and wrinkled; the lower part small, the upper part terminates in a small, straight neck, like that of a pitcher; the tail terminates in two diverging points.

134. CERCARIA CATELLUS. C. tripartita, cauda bisecta. Three-parted cercaria, the tail divided into two parts.

This animalculum is more complex in its form than many others; it has a moveable head, which is affixed to the body only by a point; an abdomen, which is not so wide, but twice as long as the head, replete with intestines; and a tail which is shorter than the head, narrower than the belly, and terminating in two bristles, which it can unite and separate at pleasure. It moves with vivacity, though without going far from its own place.

135. CERCARIA CATELINA. C. tripartita, cauda bicuspidata. Cercaria distinguished into three parts, with a short forked tail.

It differs from the preceding in several respects, being larger, the body thicker, and more cylindrical; the lower part truncated, with two short diverging points projecting from the middle. It was found in a ditch containing plenty of duck-weed.

136. CERCARIA LUPUS. C. cylindrica, elongata, torosa cauda spinis duabus. Plate XXV. Fig. 39. Cylindric cercaria, long, the tail furnished with two spines.

This animalculum is larger than most of the cercarias, and in some particulars resembles the vorticella. It is full of muscles, capable of being contracted or extended; cylindric, composed of a head, a trunk, and a tail; the head is larger than the body, the apex turned down into a little hook; the tail is like the body, but narrower, terminating in two very bright spines, which it extends in different directions; sometimes it contracts itself into one half its common size; and again extends itself as before. It was found in water among duck-weed. _a_ the head, _b_ the trunk, _c_ the tail, _d d_ the spines thereof.

137. CERCARIA VERMICULARIS. C. cylindrica annulata, proboscide exsertili, cauda spina duplici. Plate XXV. Fig. 40. Cylindrical, annulated, with a projecting proboscis, two small spines for the tail.

It is a long, cylindrical, fleshy, mutable animalculum, divided into eight or nine rings, or folding plaits; the apex either obtuse or notched into two points; the hind-part rather acute, and terminating in two pellucid thorns, between which a swelling is sometimes perceived. It often projects a kind of cloven proboscis. It is found in water where duck-weed grows. _d d_ the points of the fore-part, _e_ the proboscis.

138. CERCARIA FORCIPATA. C. cylindrica, rugosa, proboscide forcipata exsertili, cauda bicuspidata.

Cylindrical cercaria, wrinkled, with a forked proboscis, which it can extend, or retract. It is found in marshy situations.

139. CERCARIA PLEURONECTES. C. orbicularis, cauda uniseta. Orbicular, the tail consisting of one bristle.

It is membranaceous, rather round, and white. In the fore-part are two blackish points; the hind-part is furnished with a slender sharp tail; it has orbicular intestines of different sizes in the middle; the largest of them are bright. Its motion is staggering or wavering; in swimming it keeps one edge of the lateral membrane upwards; the other folded down. It is found in water which has been kept for several months.

140. CERCARIA TRIPOS. C. subtriangularis, brachiis deflexis, cauda recta. Plate XXV. Fig. 38. Cercaria somewhat of a triangular form, two bent arms, and a straight tail.

The body is flat, pellucid, and triangular, having each angle of the base or fore-part bent down into two linear arms; the apex of the triangle is prolonged into a tail. It was found in salt water; _b_, the tail; _a a_, the bent arms.

141. CERCARIA CYCLIDIUM. C. ovalis, postice subemarginata, cauda extersili. This is oval, the hind-part somewhat notched, with a tail that it thrusts out at pleasure.

It has an oval, smooth, membranaceous, and pellucid body, with a black margin. The tail is not fixed to the edge, but concealed under it, and comes out from it at every motion, but in such a manner, as to project but little from the edge. There is also a kind of border to the hinder-part. Its intestines are very pellucid vesicles. It is frequently found in pure water.

142. CERCARIA TENAX. C. membranacea, antice crassiuscula, truncata, cauda triplo breviore. Membranaceous, the fore-part rather thick, truncated, the tail three times shorter.

It is an oval, pellucid membrane, something larger than the monas lens. The fore-edge is thick and truncated, the hinder-part acute, and terminating in a short tail. It whirls about in various directions with great velocity.

143. CERCARIA DISCUS. C. orbicularis, cauda curvata. A small orbicular animalculum, with a bent tail.

144. CERCARIA ORBIS. C. orbicularis, seta caudali duplici longissima. Orbicular cercaria, with a tail consisting of two very long bristles.

145. CERCARIA LUNA. C. orbicularis, cauda lineari duplici brevi. This is likewise orbicular, with two short spines for a tail; the fore-part hollowed, so as to form a kind of crescent.