Crabs, Lobsters, Shrimps, Barnacles, etc. (Crustacea). gQ 



to floating objects; it is found in large numbers on ships, drift- 

 wood, etc. Its name of Goose-barnacles is due to the fable ac- 

 cording to which they are the young of the goose called, after 

 them, the Barnacle-goose. This myth, which is traced back to 

 the end of the 12th century, in all probability arose from the 

 desire of the priesthood of that time to increase the small range 

 of a Lenten bill of fare, by deriving the geese from marine animals. 



MoUusca. 



The term Mollusks, i. e. soft-bodied animals, is applied to 

 Snails, Slugs, Poulps, Bivalves and their allies, because they have 

 no skeleton which enters into the mechanism of their movements ; 

 neither an internal one like that of the Vertebrates, nor an ex- 

 ternal one like that of many Worms and all Crustacea. Besides 

 this point they differ from the above mentioned groups in not 

 being jointed. Very many Mollusks are provided with a shell 

 and have a head very distinctly marked off from the body and 

 bearing eyes and tentacles. 



We will begin with the highest group of the Mollusks, that of 

 the Cephalopoda or Poulps. Their head bears 8 or 10 arms or 

 feet, arranged in a ring round their mouth, and this has given rise 

 to their scientific name. Most striking" of these in the Aquarium 

 is the eight-armed Devil-fish (ital. Polpo, the Polypus of the 

 Greek) Octopus vulgaris (figs. 72 and y^), which is very common 

 on the rocky coasts of the Mediterranean. 



If one were to institute a competition for the prize of ugliness 

 between all the inhabitants of the Aquarium, the Octopus would 

 be an easy winner. In shape (or better, shapelessness), skin 

 (warty like a toad), movements — in everything is it repulsive! 

 This is an impression which can only be overcome, and indeed 

 quite changed, by close observation. 



On the sack-shaped trunk, which contains the internal organs, 

 is the head like a knob, with the two eyes and the 8 long arms, 

 moveable in every direction, extensible and bound together at 

 their bases by a broad membrane. Hidden in the middle of the 

 arms is the mouth, furnished with a pair of jaw having the form 

 of a parrot's beak. As the animal breathes, there may be noticed 

 a membranous flap which alternately opens and shuts, and laterally 

 a projecting tube ("funnel") which also opens and shuts, its move- 

 ments alternating with those of the membranous flap. The flap 

 allows the water to enter the "mantle-cavity", or hollow part 

 of the bag, in which hang the gills; the water which has been 

 used for respiration is then forced out through the "funnel", the 

 flap being kept closed. The usual mode of progression is climbing 

 and crawling by means of the arms, which thus function as feet. 

 The arms are stretched out and grasp some object by means of 

 their double row of suckers; they then shorten and draw the 



