7f> Part second. 



like aperture. These delicate jointed legs can be seen waving perpetually 

 in both Balanus and Lepas, as they so serve to create a current bringing 

 food to the mouth (see p. 53). 



Balanus forms a belt all round the rocks just at the surface of the 

 water, and these barnacles are so securely attached that they cannot be 

 washed olf by the waves. At low-tide they bear the greatest beat of the 

 sun, lasting out till high-tide with the least drop of water , which they 

 retain in their tightly closed shell. Lepas (when present, in tank Nr. 10 

 or 22) prefers to attach itself to floating objects ; it is found in large 

 numbers on ships , driftwood , etc. Its name of Goose-barnacle is due to 

 the fable according to which they are the young of the goosa called, 

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

 end of the 12 th 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. 



MOLLUSCA. 



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 external 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 of feet, arranged 

 in a ring round their mouth , and this has given rise to their scientific 

 name. Most striking cf these in the Aquarium is the eight-armed Devil- 

 fish (ital. Polpo, the Polypus of the Greek) Octopus vulgaris (Figs. 73 

 and 74), which is very common on the rocky coasts of the Mediterranean. 

 Its body has the form of a round bag, half of it is hollow and performs 

 regular respiratory contractions; at one end is a toad-like head provided 

 with two large eyes, and with eight arms united at their base by a web; 

 each arm bears two rows of suckers. Hidden in the middlle of the arms 

 is the mouth, furnished with a pair of jaws , having the form of a 

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

 nous flap which alternately opens and shuts , and laterally a projecting 

 tube ( funnel ) which also opens and shuts, its movements 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. This alternating movement 

 serves also as means of progression, the water wich is being forced out, 

 propelling the animal with its hind-end foremost (Fig. 73). The arms are 

 used for crawling and climbing , they serve also to catch and hold the 



