Mollusca. 



qi 



make more frequent use of them. The sepia used by artists is the 

 product of a gland, the so-called ink-sack, the contents of which 

 can be squirted out through the funnel ; a small quantity is enough 

 suddenly to envelop the animal in a black cloud, which hides it 

 from its pursuer. The ink is extracted, dried and brought to 

 market ; even that of fossil species can still be used. — The wonder- 

 ful play of colours on the living animal is due to large cells (chro- 

 matophores) which are situated in the skin and are filled with 

 finely divided dark colouring matter; as these cells contract 

 (become globular) and expand (become flat), a continuous change 

 of colours takes place. Stripes, spots and markings make their ap- 

 pearance and disappear again according as the animal is at rest or 

 is irritated. The Cuttlefish have complete control over this change 

 of colours. This is seen from the protective colouring, which they 

 assume when they lie on the sand or on dark rocky ground ; in either 

 case they can hardly be distinguished. — The males court the 

 females with great ardour, and in their excited state produce 

 most brilhant colours over their body. The female lays large, 

 black, pear-shaped eggs and fixes them singly to corals and algae, 

 usually close together, so that they form large grape-like clusters 

 (often visible in tank Nr. 19). As soon as the young are hatched 

 they show their proficiency in changing their colouring and emit- 

 ting the sepia. 



The Cuttlefish is an important article of commerce: its flesh 

 is eaten, if with less relish than that of the Octopus or Squid. 

 The cuttle-bone is used for polishing wood and as tooth-powder. 

 Besides catching them with ground-nets and spears, the fishermen 

 make use of two peculiarities of the animals; they decoy the 

 females by placing Pistacia twigs in the water, on which they 

 lay their eggs for preference, and alure the males by towing a 

 living female on a line behind a rowing boat. 



The Calmar or Squid (Loligo vulgaris, fig. 15), very common 

 in winter, is unfortunately very delicate for the Aquarium. Like 

 a swarm of birds, slowly beating their fins, these transparent 

 animals swim backwards and forwards, without turning round, 

 until they die, usually only a few days after their capture. The 

 slightest disturbance puts them in a state of great alarm and 

 causes their milk-white bodies to show the most lovely red tints. 

 Noticeable for their size are the large iridescent eyes. The eyes of 

 Cephalopods are relatively and absolutely larger than those of 

 any other known animal. The weight of the eyes can be 1/4 that 

 of the body and a giant "Kraken" caught off Ireland had eyes 

 15 inches in diameter. They can be fed with small shrimps and 

 will be seen to use their long arms like the cuttlefish. Their flesh 

 is eaten very generally; the "pen" — corresponding to the cuttle- 

 bone — is translucent, flexible and shaped like a feather. Like 

 Sepia they secrete ink; hence the Italian name of calaniajo (ink-pot). 



