52 



OUTLINES OP NATURAL HISTORY. 



rudely touclied, it contracts itself forcibly, and squirts 

 out a jet of water from both necks. 



Fig 21. — A, AseicUa (Pliallusia) mentuhi. Two individuals attached to 

 the inner surface of an Oyster-shell, natural size. B, Diagraminatio 

 section of tlie same : a Opening by which the water enters ; b Opening 

 by which the water escapes ; p Respiratory chamber ; g Gullet ; s 

 Stomach ; i Intestine ; v Vent ; c Chamber into which the water es- 

 capes after passing through the respiratory sac; h Heart ; t Outer layer 

 of the integument ; if Inner muscular layer or " tunic." 



The outer covering of the body (fig. 21, B, t) is of a 

 leathery nature, but is nevertheless partially translucent, 

 especially in the neighbourhood of the necks. It is re- 

 markable for containing a substance apparently identical 

 with the woody fibre of vegetables. This outer covering 

 is loosely Mned by an inner layer or "tunic" (f) which 

 is of a highly muscular nature, and which confers upon 

 the animal its power of squirting out water. 



The highest of the two necks of the animal (fig. 21, 

 B, a) is perforated by an opening surrounded by eight 

 lobes, at the bases of which is a series of rudimentary eyes, 

 in the form of yellow spots, each with a red point in its 



