The royal natural history . eggs and larva OF Mermis (enlarged). Arrow-Worms,—Order ChvETOGnatha. The small group of worms included under this heading are of doubtful are glass-like, transparent creatures living in the sea, near the surface ofwhich they swim in numbers. They are most active and vigorous swimmers, as NEMERTINE WORMS. 457 might be expected from their slender build, and .the presence of a large horizontalfin at the sides of the hinder half of the body, projecting beyond the tail. Theshape of the body and the presence of the large tail-fin suggested the name Sagitta.
The royal natural history . eggs and larva OF Mermis (enlarged). Arrow-Worms,—Order ChvETOGnatha. The small group of worms included under this heading are of doubtful are glass-like, transparent creatures living in the sea, near the surface ofwhich they swim in numbers. They are most active and vigorous swimmers, as NEMERTINE WORMS. 457 might be expected from their slender build, and .the presence of a large horizontalfin at the sides of the hinder half of the body, projecting beyond the tail. Theshape of the body and the presence of the large tail-fin suggested the name head is bluntly rounded and furnished with a pair of eyes, a pair of feelers. arrow-worm (25 times nat. size). and an armature of close-set horny teeth, all of which must be of the greatestservice to the animal in its roving, predaceous life. The Nemertine Worms,—Class Nemertinea. All the members of this group are characterised by having the body elongateand flattened, at least on the abdominal side; at the front end there are frequentlytwo clusters of eyes, and two apertures, one of which leads into the alimentarycanal, and the other into a cavity containing a peculiar organ known as theproboscis. The latter, which is used as an instrument for prehension, can be thrustout with swiftness to a considerable distance, and in many species is armed in themiddle with a sharp spike-like tooth and some smaller ones at the sides, which arebrought by degrees into use as the large median one is wornaway or fractured. This organ is shown protruded in a smallmarine species (Tetrastemma obscurum) in the illustration onthis page, and retracted within the body in the full il
Size: 3122px × 801px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
