Earth-worms are found throughout the world. Though few in genera, and not many in species, yet they make up in individual numbers, for it has been estimated that they average about one hundred thousand to the acre. Our American species have never been monographed, which renders it impossible to judge of their probable number. Their castings may be seen on commons, so as to cover almost entirely their surface, where the soil is poor and the grass short and thin, and they are almost as numerous in some of our parks where the grass grows well and the soil appears rich.
Pear-shaped cells are set round a felt-work of nerve-fibrils (neuropil). A neuro-sensory cell is shown with one fibre directed peripherally, branching on the surface; and one directed centrally, ramifying in the neuropil. Several very slender fibrils from the neuropil pass up the stalk of each ganglion-cell. They join a network near its surface. This net is connected by radiating fibrils with a coarser net which surrounds the nucleus. From the central net a relatively stout fibril passes to muscle-fibres.
In the Serpulacees ( Serpulacea ), the gills are located entirely at the front end of the body; the cilia that coat her cause a current to flow into the water, which supplies food to the mouth opening immediately below it. The head segment is not separated from the mouth segment, as is the case with most other Ringworms, but has grown together with it.
The third group of tube worms is formed by the gillheads ( Cephalobranchiata ), so called, because the softened thread or tree-shaped appendages for breathing are at the head or at least at the anterior segments. They inhabit tubes from which they never emerge voluntarily. Accordingly, the appendages of most segments, except the anterior ones, are much less developed than those of the free-living many-bristles, and the way of life is more peaceful, as evidenced by the absence of dental plates in the oral cavity.
Tube dwellers without gills ( Abranchiata ) include the Bristleworms ( Chaetopterus), which differ markedly from all other members of the order and represent a separate family. With them, too, the body consists of three uneven divisions. The head of the species shown here is funnel-shaped, cut at the back and fitted with two probes here. The following 9 segments have elongated, flat foot stubs, which bear a bundle of brown brushes at the top edge. Very remarkable is the shape of the 5 segments of the middle section. The last 3 are missing the top foot stubs; those of the first two form a comb on the middle of the back with 2 feel-like protrusions, which extend far over the front part of the back. The lower stubs on the first segment are broad, curled towards the belly and joined here; on the other 4 segments they have a triangular shape and a sideways direction. The second segment is very swollen and purplish black in color. The posterior body part consists of about 50 members, which shine very wide due to the strongly laterally extended foot stubs. The animal in question was found in deep water on the coast of Normandy and in the Mediterranean Sea. It reaches 22 cm in length. and is surrounded by a 32 cM. long sleeve, made of a multi-layered material, resembling coarse, yellowish parchment.
One of the most common species in the Mediterranean. These Worms have a very graceful, glistening appearance, after being rinsed from the dirt, which usually covers their bodies in large quantities, by repeated rinsing. However, the beautiful Hermione's thorns are more fearful than those of the Porcupine ( Hystrix), there barbs hold them back in the skin with which they come into contact. Predatory fish do not care much about these weapons.
Like all other Oligochaetes, Earthworms are androgynous. The genitals are usually in the 9th to 15th segments. In this same body division, the Lumbricides red blood-filled closed vasculature, which sometimes partially shimmers through the skin, has particularly wide, beating ringing vessels that connect the two large blood vessels above and below the digestive tract. A little further back, about the middle of the front half of the body, you will notice the girdle during the reproductive period, especially in spring. This organ, necessary for mating, is characterized by skin glands, which secrete a lot of mucus and is formed by swelling of the back and sides of 6 to 10 rings; depending on the species, its color varies from whitish or yellowish to red and brown. The species are also distinguished by the position of the belt; it begins between the 20th and 30th segments. The eggs are laid in a slime layer formed by glands of the belt, which surrounds the body in an annular manner; from this mucous layer, after the Worm has stripped it of itself, a cocoon with a horny wall, containing several eggs, only hatches.
In the adult state, this animal reaches a length of 20 cM. It is said to emit light by phosphorescence.
The species depicted lives in the Mediterranean Sea at 1 or 2 fathoms. The ovoid anterior section of the elongated, cylindrical, slimy body, the glans , is separated from the subsequent collar by a deep constriction, in which the mouth opening is located. The glans, whose large internal cavity can be filled and emptied with water through two openings, changes its shape and size; it serves, except as a suture when crawling, as a drill when digging passages in the sea bed, in which the body is usually hidden up to the mouth. The alimentary canal, in which, in addition to food, water is also absorbed, is in communion with two longitudinal series of gill pouches , which are located in the anterior or gill part of the trunk on the back. The water, which has been used for breathing, flows out through a series of about 20 fine slits on the ventral side. The widest part of the alimentary canal is in the stomach part of the trunk; it is always filled with sand, the organic components of which serve the animal as food. The tail is grooved annularly; through the terminal vent opening, the sand is ejected, which forms piles next to the opening of the corridor.
The place that the Bridgeworms or Starworms ( Gephyrei ) should occupy in the system has been subject to a great difference of opinion. By some zoologists they were counted among the Echinoderms, others among the Worms, either among the Annelids or the Acanthocephalus.
Bonellia viridis, recognizable by its two-winged snout, lives in the Mediterranean Sea and on the Canadian coast, hidden between gravel and rock crevices. A green dye penetrates both the muzzle and the other body. This is covered with many warts and can constrict and contract in many ways. The snout is, if possible, suitable for even greater shape changes, since it is large in size of about 8 cm. body length, more than 50 cM. can be extended far and only when contracted[ 637 ]a few cM. is long. The mouth opening is a cervical longitudinal groove at the root of the snout. Occasionally the Bonellia leaves her hiding corner and crawls over the bottom with the help of her snout, the front horns of which act as sutures. The great flexibility of the body allows it to use very narrow crevices for shelter; she is averse to full daylight, likes the twilight of the morning better. The males, which have only recently become known as such, have a completely different appearance than the females, are tiny and resemble Turbellaria.
Elegant Flower Polyp ( Floscularia ornata ), at 200-fold enlargement.
Ornamental Flower Polyp ( Floscularia ornata ) depicted is a representative of a last large family, known as Tube inhabitants ( Tubicolariae), since they are, at least for the most part, surrounded by a shell. The most remarkable phenomenon they offer is the very strong modification of their gear. On five conical protrusions from the head edge one sees bundles of long hair, which do not deserve the name of cilia, because they are stiff and almost immobile. Almost in the funnel of the mouth is the ring of cilia, which supplies food to the animal. This is surrounded by a fine, jelly-like tube, into which it, like the members of related genera, can retract by sliding the foot together.
Four-horned Tortoise ( Noteus quadricornis ), at 300-fold magnification.
We choose as an example the four-horned turtle bearer ( Noteus quadricornis ) of the family of turtle animals ( Loricata ), characterized by the hard, shield-shaped armor surrounding their compressed body from top to bottom. In our species, it is gracefully carved from the front and fitted with 4 horn-like protrusions. The front part of the body is covered with a soft skin and can be completely retracted under this armor. When swimming and eating, the animal unfolds its radar organ; this consists of two half-saucer-shaped, fleshy lobes, which are retracted by muscles and can be pushed out of the body cavity by squeezing blood; its free edge is set with a series of delicate eyelashes, which randomly vibrates the animal; the whole gear then makes the impression of two wheels on many Rotary animals, which rotate quickly on their axis.