Worm Externals

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Worm Externals
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Worm Externals

• The most obvious externals of the earthworm are
  those parts which are absent. The worm has no
  obvious head or appendages. Appendages are parts
  which are added on like the arms, legs, and
  antennae. Because of this, we must identify worm
  parts by segments or somite numbers.

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Worm Externals

• We will also use scientific terms when giving
  directions. The upper side of the worm is called
  DORSAL. The belly side of the worm is called
  VENTRAL. The head end of the worm is called
  the ANTERIOR end and is always at the end closest
  to the ring around the worm. The tail end of
  the worm is called the POSTERIOR end and is
  located further from the ring around the worm.

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Worm Externals

• Anterior End Head end of worm Posterior End
  Tail end of worm

Dorsal Side Upperside or backside of worm
Ventral View Belly side of worm
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Worm Externals

• Anus Posterior, excretes feces

Mouth Anterior, food enters and begins breaking
down
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Worm Externals

• Clitellum used in reproduction, secretes mucus

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Worm Externals

• Prostomium anterior and dorsal used to dig
• Peristomium anterior and ventral chin

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Worm Externals

• Setae Ventral tiny hairs used in locomotion
• Male Genital Pores Somite 15 secretes sperm
• - Somite 14 contains the oviducts (eggs)

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Worm Externals

• The best way to study this animal is to make
  comparisons to the similar parts of a human. If
  a part is the same and it does the same job, we
  will call it HOMOLOGOUS. If the part is not the
  same but does the same job we will call it
  ANALOGOUS.

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DISSECTION

• In order to dissect the worm, the small muscles
  (septa muscles) which hold the skin on must be
  sliced. The skin is then pulled back and pinned
  to the tray to exposes all internal organs. Be
  slow and thorough in your dissection. Your are
  not just cutting for cutting sake. You will be
  using tools which are properly called a probe, a
  scalpel, and forceps.