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But in the annelid and all higher forms a special system of tubes has developed to carry the nutriment, and usually oxygen also, needed to keep up the combustion required to furnish the energy in these active organs.
Omitting structures whose organic nature has been questioned, there are left to mention a tiny seashell of one of the most lowly types, a DISCINA from the pre- Cambrian rocks of the Colorado Canyon, and from the pre-Cambrian rocks of Montana trails of annelid worms and casts of their burrows in ancient beaches, and fragments of the tests of crustaceans.
They have been called by Professor Sedgwick the Longmynd or Bangor Group, comprising, first, the Harlech and Barmouth sandstones; and secondly, the Llanberis slates. Histioderma Hibernica, Kinahan. Oldhamia beds. Bray Head, Ireland. 1. Showing opening of burrow, and tube with wrinklings or crossing ridges, probably produced by a tentacled sea worm or annelid. 2.
The descent of the Vertebrates from the Articulates has been maintained by a number of zoologists during the last thirty years with more zeal than discernment; and, as a vast amount has been written on the subject, we must deal with it to some extent. The most popular of these hypotheses was the annelid theory, which derived the Vertebrates from the Worms.
CROSS-SECTION OF BODY SEGMENT OF ANNELID. LANG. dp and vp, dorsal and ventral halves of parapodia; b and ac, bristles; k, gill; dc and vc, feelers; rm, lateral muscles; lm, longitudinal muscles; vd, dorsal blood-vessel; vo, ventral blood-vessel; bm, ventral ganglion; ov, ovary; tr, opening of nephridium in the perivisceral cavity; np, tubular portion of nephridium.
In the annelid they are projections of the parapodia, in the mollusk expansions of the skin, where the foot or creeping sole joins the body. Why did the vertebrate take a new and strange, and, at first sight, disadvantageous mode of breathing? There must have been some good reason for this.
An excretory system has appeared to carry off the waste of the muscles and nerves. In the schematic worm and annelid the reproductive system is simpler, though perhaps equally effective. It takes the excess of nutriment of the body. The muscular system has taken the form of a sack composed of longitudinal and transverse fibres.
This period extends from the beginning of life up to the time when the annelid was the highest living form yet developed. But in insects and lower vertebrates another system has risen to dominance. This is muscle. The vertebrate no longer devotes all, or the larger part, of its income to digestion and reproduction. If it did, it would degenerate or disappear.
Cambrian conglomerate and sandstone. 3, 3'. Quartzose Lower Silurian, with annelid burrows. 3a. Fossiliferous Silurian limestone. 3b.
Perhaps it is not too much to say that the eidoscopic eye first awakened the slumbering animal mind, for its reflex effect upon the supra-oesophageal ganglion cannot be over-estimated. The animal will very soon begin to think. Between the turbellarian and the annelid many aberrant lines diverged.
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